Filed Pursuant to Rule 424(b)(3)
Registration No. 333-221500

PROSPECTUS SUPPLEMENT

(To Prospectus dated November 17, 2017)

Common Stock

4,500,000 Shares of Our Common Stock Offered by the Selling Stockholders

The selling stockholders identified in this prospectus supplement are offering 4,500,000 shares of our common stock. We will not receive any proceeds from the sale of the shares to be offered by the selling stockholders.

Our common stock is listed on the NASDAQ Global Select Market under the symbol “BL.” On December 4, 2017, the last reported sale price of our common stock on the NASDAQ Global Select Market was $35.80 per share.

Following this offering, our Principal Stockholders (as defined herein) will control more than a majority of the voting power of our common stock and we will continue to be a “controlled company” within the meaning of the corporate governance rules of the NASDAQ Stock Market. We have elected not to take advantage of the “controlled company” exemption.

The underwriters have agreed to purchase shares of our common stock from the selling stockholders at a price of $34.07 per share, which will result in approximately $153,315,000 of aggregate proceeds to the selling stockholders, before expenses. The underwriters propose to offer the shares of common stock from time to time for sale in one or more transactions on the Nasdaq Global Select Market, in the over-the-counter market, through negotiated transactions or otherwise, at market prices prevailing at the time of sale, at prices related to such prevailing market prices or negotiated prices.

To the extent that the underwriters sell more than 4,500,000 shares of common stock, the underwriters have the option to purchase up to an additional 675,000 shares from the selling stockholders identified in this prospectus at a price of $34.07 per share.

We are an “emerging growth company” as defined under the federal securities laws, and, as such, may elect to comply with certain reduced public company reporting requirements for this and future filings.

Investing in our common stock involves risks. Please carefully read the information under the headings “Risk Factors ” beginning on page S-9 of this prospectus supplement and “Item 1A—Risk Factors” of our most recent report on Form 10-K or 10-Q that is incorporated by reference in this prospectus supplement before you invest in our securities.

Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement and the accompanying prospectus. Any representation to the contrary is a criminal offense.

The underwriters expect to deliver the shares of common stock to purchasers on or about December 7, 2017.

J.P. Morgan

December 4, 2017

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement and the accompanying prospectus form part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this common stock offering and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference therein. The second part, the accompanying prospectus, provides more general information. Generally, when we refer to this prospectus, we are referring to both parts of this document combined. We urge you to carefully read this prospectus supplement and the accompanying prospectus, and the documents incorporated herein and therein, before buying any of the securities being offered under this prospectus supplement. To the extent that any statement that we make in this prospectus supplement is inconsistent with statements made in the accompanying prospectus or any documents incorporated by reference therein, the statements made in this prospectus supplement will be deemed to modify or supersede those statements made in the accompanying prospectus and documents incorporated by reference therein.

We, the selling stockholders and the underwriters have not authorized anyone to provide any information or to make any representations other than those contained in this prospectus supplement and the accompanying prospectus, which together we sometimes refer to generally as the prospectus, or in any free writing prospectuses prepared by us or on our behalf or to which we have referred you. We, the selling stockholders and the underwriters take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We, the selling stockholders and the underwriters are not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should not assume that the information contained in this prospectus supplement and the accompanying prospectus or the documents incorporated herein and therein by reference is accurate as of any date other than their respective dates. Our business, financial condition, and results of operations may have changed since those dates. It is important for you to read and consider all information contained in this prospectus supplement and the accompanying prospectus, including the documents incorporated by reference herein and therein, and any related free writing prospectus, in making your investment decision. You should also read and consider the information in the documents to which we have referred you in the sections entitled “Where You Can Find Additional Information” and “Information Incorporated by Reference” in this prospectus supplement and in the accompanying prospectus.

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RISK FACTORS

An investment in our common stock involves a high degree of risk. Prior to making a decision about investing in our common stock, you should carefully consider the risks, uncertainties and assumptions discussed under “Part I—Item 1A—Risk Factors” in our most recent Annual Report on Form 10-K or under “Part II—Item 1A—Risk Factors” in our Quarterly Reports on Form 10-Q and in other documents, which are incorporated herein by reference into this prospectus supplement and accompanying prospectus. The risks and uncertainties we have described are not the only ones we face. Additional risks and uncertainties not presently known to us or that we currently deem immaterial may also affect our operations. If any risks actually occur, our business, financial condition and results of operations may be materially and adversely affected. In such an event, the trading price of our common stock could decline and you could lose part or all of your investment.

For more information about our SEC filings, please see “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus supplement and the accompanying prospectus contain forward-looking statements within the meaning of the federal securities laws, which statements involve substantial risks and uncertainties. Forward-looking statements generally relate to future events or our future financial or operating performance. In some cases, you can identify forward-looking statements because they contain words such as “may,” “will,” “should,” “expects,” “plans,” “anticipates,” “could,” “intends,” “target,” “projects,” “contemplates,” “believes,” “estimates,” “predicts,” “potential” or “continue” or the negative of these words or other similar terms or expressions that concern our expectations, strategy, plans or intentions. Forward-looking statements contained in this prospectus supplement and the accompanying prospectus include, but are not limited to, statements about:

We caution you that the foregoing list may not contain all of the forward-looking statements made in this prospectus supplement and the accompanying prospectus.

You should not rely upon forward-looking statements as predictions of future events. We have based the forward-looking statements contained in this prospectus supplement and the accompanying prospectus primarily on our current expectations and projections about future events and trends that we believe may affect our business, financial condition, results of operations and prospects. The outcome of the events described in these forward-looking statements is subject to risks, uncertainties and other factors described in the section titled “Risk Factors” and elsewhere in this prospectus supplement and the accompanying prospectus. Moreover, we operate in a very competitive and rapidly changing environment. New risks and uncertainties emerge from time to time and it is not possible for us to predict all risks and uncertainties that could have an impact on the forward-looking statements contained in this prospectus supplement and the accompanying prospectus. We cannot assure you that the results, events and circumstances reflected in the forward-looking statements will be achieved or occur, and actual results, events or circumstances could differ materially from those described in the forward-looking statements.

The forward-looking statements made in this prospectus supplement and the accompanying prospectus relate only to events as of the date on which the statements are made. We undertake no obligation to update any forward-looking statements made in this prospectus supplement and the accompanying prospectus to reflect events or circumstances after the date of this prospectus supplement and the accompanying prospectus or to reflect new information or the occurrence of unanticipated events, except as required by law. We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements and you should not place undue reliance on our forward-looking statements. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures or investments we may make.

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USE OF PROCEEDS

We will not receive any of the proceeds from the sale of shares of common stock by the selling stockholders.

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MARKET PRICE OF COMMON STOCK

Our common stock has been traded on the NASDAQ Global Select Market under the symbol “BL” since October 28, 2016. Prior to that time, there was no public market for our common stock. The following table sets forth, for the periods indicated, the high and low intraday sales prices for our common stock as reported on the NASDAQ Global Select Market.

On December 4, 2017, the last reported sales price on the NASDAQ Global Select Market for our common stock was $35.80 per share.

Holders of Record

As of September 30, 2017, there were 30 shareholders of record. The number of record holders does not include beneficial holders who hold their shares in “street name,” meaning that the shares are held for their accounts by a broker or other nominee. Accordingly, we believe that the total number of beneficial holders is higher than the number of our shareholders of record.

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DIVIDEND POLICY

We have never declared or paid, any cash dividends on our common stock. We currently intend to retain all of our future earnings, if any, to finance our operations and do not anticipate paying any cash dividends on our common stock in the foreseeable future. Any future determination as to the declaration and payment of dividends will be at the discretion of our board of directors and will depend on then-existing conditions, including our financial condition, operating results, contractual restrictions, capital requirements, business prospects, and other factors our board of directors may deem relevant.

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MATERIAL U.S. FEDERAL INCOME AND ESTATE TAX CONSEQUENCES TO NON-U.S. HOLDERS OF OUR COMMON STOCK

The following is a summary of the material U.S. federal income and estate tax consequences to non-U.S. holders (as defined below) of the ownership and disposition of our common stock but does not purport to be a complete analysis of all the potential tax considerations relating thereto. This summary is based upon the provisions of the Internal Revenue Code of 1986, as amended, or the Code, U.S. Treasury regulations promulgated thereunder, administrative rulings and judicial decisions, all as of the date hereof. These authorities may be changed, possibly retroactively, so as to result in U.S. federal income and estate tax consequences different from those set forth below. We have not sought and will not seek any ruling from the Internal Revenue Service, or the IRS, with respect to the statements made and the conclusions reached in the following summary, and there can be no assurance that the IRS will agree with such statements and conclusions.

This summary applies only to common stock acquired in this offering. It does not address the tax consequences arising under the laws of any non-U.S., state or local jurisdiction or under U.S. federal gift and estate tax laws, except to the limited extent set forth below. In addition, this discussion does not address the potential application of the alternative minimum tax, the tax on net investment income or any other tax considerations applicable to an investor’s particular circumstances or to investors that may be subject to special tax rules, including, without limitation:

In addition, if any entity classified as a partnership for U.S. federal income tax purposes holds our common stock, the tax treatment of a partner generally will depend on the status of the partner and upon the activities of the partnership. Accordingly, partnerships that hold our common stock, and partners in such partnerships, should consult their tax advisors regarding the tax consequences of the purchase, ownership and disposition of our common stock.

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You are urged to consult your tax advisor with respect to the application of the U.S. federal income tax laws to your particular situation, as well as any tax consequences of the purchase, ownership and disposition of our common stock arising under the U.S. federal estate or gift tax laws or under the laws of any state, local, non-U.S. or other taxing jurisdiction or under any applicable tax treaty.

Non-U.S. Holder Defined

For purposes of this discussion, except as modified for estate tax purposes, you are a non-U.S. holder if you are a beneficial owner of shares of our common stock other than a partnership or other entity classified as a partnership for U.S. federal income tax purposes, or:

Distributions

We do not plan to make any distributions on our common stock. However, if we do make distributions on our common stock, those payments will constitute dividends for U.S. tax purposes to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. To the extent those distributions exceed both our current and our accumulated earnings and profits, they will constitute a return of capital and will first reduce your basis in our common stock, but not below zero, and then will be treated as gain from the sale of stock.

Subject to the discussion below on effectively connected income, any dividend paid to you generally will be subject to U.S. withholding tax either at a rate of 30% of the gross amount of the dividend or such lower rate as may be specified by an applicable income tax treaty. In order to receive a reduced treaty rate, you must provide us with an IRS Form W-8BEN, IRS Form W-8BEN-E or other appropriate version of IRS Form W-8, including a U.S. taxpayer identification number, if required, certifying qualification for the reduced rate. A non-U.S. holder of shares of our common stock eligible for a reduced rate of U.S. withholding tax pursuant to an income tax treaty may obtain a refund of any excess amounts withheld by timely filing an appropriate claim for refund with the IRS. If the non-U.S. holder holds the stock through a financial institution or other agent acting on the non-U.S. holder’s behalf, the non-U.S. holder will be required to provide appropriate documentation to the agent, which may then be required to provide certification to the relevant paying agent, either directly or through other intermediaries.

Dividends received by you that are effectively connected with your conduct of a U.S. trade or business (and, if required by an applicable tax treaty, that are attributable to a permanent establishment maintained by you in the U.S.), are generally exempt from such withholding tax. In order to obtain this exemption, you must provide us with an IRS Form W-8ECI properly certifying such exemption. Such effectively connected dividends, although not subject to withholding tax, generally are taxed at the same graduated rates applicable to U.S. persons, net of certain deductions and credits. In addition, if you are a corporate non-U.S. holder, dividends you receive that are effectively connected with your conduct of a U.S. trade or business may also be subject to a branch profits tax at a rate of 30% or such lower rate as may be specified by an applicable income tax treaty. You should consult your tax advisor regarding any applicable tax treaties that may provide for different rules.

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Gain on Disposition of Our Common Stock

Subject to discussions below regarding backup withholding and foreign accounts, you generally will not be required to pay U.S. federal income tax on any gain realized upon the sale or other disposition of our common stock unless:

We believe that we are not currently and will not become a USRPHC. However, because the determination of whether we are a USRPHC depends on the fair market value of our U.S. real property relative to the fair market value of our other business assets, there can be no assurance that we will not become a USRPHC in the future. Even if we become a USRPHC, however, as long as our common stock is regularly traded on an established securities market, such common stock will be treated as U.S. real property interests only if you actually or constructively hold more than 5% of such regularly traded common stock at any time during the shorter of the five year period preceding your disposition of, or your holding period for, our common stock.

If you are a non-U.S. holder described in the first bullet above, you will be required to pay U.S. federal income tax on the net gain derived from the sale under regular graduated U.S. federal income tax rates, and a corporate non-U.S. holder described in the first bullet above also may be subject to the branch profits tax at a 30% rate, or such lower rate as may be specified by an applicable income tax treaty. If you are an individual non-U.S. holder described in the second bullet above, you will be required to pay a flat 30% U.S. federal income tax (or such lower rate specified by an applicable income tax treaty) on the gain derived from the sale, which gain may be offset by U.S.-source capital losses for the year. You should consult your tax advisor regarding any applicable income tax or other treaties that may provide for different rules.

Federal Estate Tax

Our common stock beneficially owned by an individual who is not a citizen or resident of the United States (as defined for U.S. federal estate tax purposes) at the time of their death will generally be includable in the decedent’s gross estate for U.S. federal estate tax purposes, unless an applicable estate tax treaty provides otherwise.

Backup Withholding and Information Reporting

Generally, we must report annually to the IRS the amount of dividends paid to you, your name and address, and the amount of tax withheld, if any. A similar report will be sent to you. Pursuant to applicable income tax treaties or other agreements, the IRS may make these reports available to tax authorities in your country of residence.

Payments of dividends on or of proceeds from the disposition of our common stock made to you may be subject to additional information reporting and backup withholding at a current rate of 28% unless you establish an exemption, for example, by properly certifying your non-U.S. status on a Form W-8BEN, IRS Form W-8BEN-E or another appropriate version of IRS Form W-8. Notwithstanding the foregoing, backup

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withholding and information reporting may apply if either we or our paying agent has actual knowledge, or reason to know, that you are a U.S. person.

Backup withholding is not an additional tax; rather, the U.S. federal income tax liability of persons subject to backup withholding will be reduced by the amount of tax withheld. If withholding results in an overpayment of taxes, a refund or credit may generally be obtained from the IRS, provided that the required information is furnished to the IRS in a timely manner.

Foreign Account Tax Compliance Act (FATCA)

Provisions commonly referred to as “FATCA” impose a U.S. federal withholding tax of 30% on dividends on and the gross proceeds from a disposition of our common stock to a “foreign financial institution” (as specifically defined in the Code) unless such institution enters into an agreement with the U.S. government to, among other things, withhold on certain payments and to collect and provide to the U.S. tax authorities substantial information regarding U.S. account holders of such institution (which includes certain equity and debt holders of such institution, as well as certain account holders that are foreign entities with U.S. owners) or otherwise establishes an exemption. A U.S. federal withholding tax of 30% generally applies to dividends on and the gross proceeds from a disposition of our common stock to a “non-financial foreign entity” (as specifically defined in the Code) unless such entity provides the withholding agent with either a certification that it does not have any substantial direct or indirect U.S. owners or provides information regarding direct and indirect U.S. owners of the entity or otherwise establishes an exception. The withholding provisions described above generally apply to payments of dividends on our common stock and, under applicable Treasury Regulations and administrative guidance, are expected to apply to payments of gross proceeds from a sale or other disposition of such common stock on or after January 1, 2019. An intergovernmental agreement between the United States and an applicable foreign country may modify the requirements described in this paragraph. Under certain circumstances, a non-U.S. holder might be eligible for refunds or credits of such taxes. You should consult your tax advisors regarding the potential application of FATCA to your investment in our common stock.

Each prospective investor should consult its tax advisor regarding the particular U.S. federal, state and local and non-U.S. tax consequences of purchasing, holding and disposing of our common stock, including the consequences of any proposed change in applicable laws.

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SELLING STOCKHOLDERS

The following table details the name of each selling stockholder, the number of shares of our common stock beneficially owned by the selling stockholder, and the number of shares of our common stock being offered by the selling stockholder for sale under this prospectus supplement (assuming no exercise of the underwriters’ option to purchase additional shares). The percentage of shares of our common stock beneficially owned by the selling stockholders both prior to and following the offering of securities pursuant to this prospectus supplement, is based on 52,936,721 shares of our common stock outstanding as of November 30, 2017.

Shares of common stock subject to options currently exercisable or exercisable within 60 days of November 30, 2017 which are subject to vesting conditions expected to occur within 60 days of November 30, 2017 are deemed to be outstanding and beneficially owned by the person holding the options for the purpose of computing the percentage of beneficial ownership of that person and any group of which that person is a member, but are not deemed outstanding for the purpose of computing the percentage of beneficial ownership for any other person.

Unless otherwise indicated in the footnotes below, each stockholder named in the following table possesses sole voting and investment power over the shares listed. The information does not necessarily indicate beneficial ownership for any other purpose. Unless otherwise noted below, the address of each stockholder listed on the table is c/o BlackLine, Inc., 21300 Victory Boulevard, 12^th Floor, Woodland Hills, CA 91367.

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No selling stockholder has had any material relationship with us or any of our affiliates within the past three fiscal years, other than as described below. The following is a summary of transactions since January 1, 2014 to which we have been or will be a party, in which the amount involved exceeded or will exceed $120,000, and in which any of the selling stockholders, or any immediate family member of, or person sharing the household with, any of these individuals or entities, had or will have a direct or indirect material interest.

Stockholders’ Agreement

We are party to the Stockholders’ Agreement, which contains specific rights, obligations and agreements of our Principal Stockholders as owners of our common stock. In addition, the Stockholders’ Agreement contains provisions related to the composition of our board of directors and its committees.

Voting Agreement. Under the Stockholders’ Agreement, our Principal Stockholders have agreed to take all necessary action, including casting all votes to which such existing owners are entitled to cast at any annual or special meeting of stockholders, so as to ensure that the composition of our board of directors and its committees complies with (and includes all of the nominees in accordance with) the provisions of the Stockholders’ Agreement related to the composition of our board of directors and its committees.

Silver Lake Sumeru Approvals. Under the Stockholders’ Agreement and subject to our amended and restated certificate of incorporation and amended and restated bylaws, and applicable law, for so long as the Principal Stockholders collectively own or hold of record, directly or indirectly, in the aggregate at least 40% of their collective “Post-IPO Shares” (as defined in the Stockholders’ Agreement), as adjusted for any reorganization, recapitalization, stock dividend, stock split, reverse stock split or similar changes in the Company’s capitalization, the following actions will require the approval of our board of directors, including the affirmative vote of at least two Silver Lake Sumeru directors:

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Transfer Restrictions. Under the Stockholders’ Agreement, each of Iconiq, Ms. Tucker and Mr. Spanicciati have agreed, subject to certain limited exceptions, not to transfer, sell, exchange, assign, pledge, hypothecate, convey or otherwise dispose of or encumber any shares of our common stock without the consent of Silver Lake Sumeru until the earlier of (i) two years following the completion our initial public offering, or November 2, 2018, and (ii) Silver Lake Sumeru’s reduction of its holdings of common stock following our initial public offering by 50%; provided, however, that Iconiq and Mr. Spanicciati have the right to sell all of the shares of our common stock offered by each in this offering, Iconiq, Ms. Tucker and Mr. Spanicciati have the right to sell all of the shares of our common stock offered by each for resale under the accompanying prospectus, and in addition, Ms. Tucker and Mr. Spanicciati will each have the right to sell a number of shares equal to up to 1% of the total outstanding shares of our common stock annually pursuant to Rule 144 of the Securities Act.

Drag Along Right. For so long as Silver Lake Sumeru holds greater than 10% of our common stock then outstanding, if Silver Lake Sumeru approves a change of control transaction, each of Iconiq, Ms. Tucker and Mr. Spanicciati will be required to vote in favor of and not oppose such transaction and, if structured as a sale of shares, sell its shares to a prospective buyer on the same terms that are applicable to Silver Lake Sumeru.

Registration Rights Agreement

We are party to an Amended and Restated Registration Rights Agreement with our Principal Stockholders, dated as of October 27, 2016, or the Registration Rights Agreement. Under the Registration Rights Agreement our Principal Stockholders are entitled to rights with respect to the registration of their shares under the Securities Act. All of the shares of our common stock to be sold by the selling stockholders in this offering will be sold pursuant to the Registration Rights Agreement. We will pay the registration expenses (other than underwriting discounts and commissions and stock transfer taxes) of the holders of the shares registered pursuant to the registrations described below.

Silver Lake Sumeru will be entitled to certain S-1 and S-3 registration rights on one or more other occasions. In addition, Iconiq is entitled to certain S-3 registration rights on one or more occasions. Beginning two years following the completion of our initial public offering, or November 2, 2018, Ms. Tucker and Mr. Spanicciati will also be entitled to certain S-3 registration rights on one or more occasions. In addition, if we or a Principal Stockholder proposes to register the offer and sale of our capital stock under the Securities Act, the other Principal Stockholders will be entitled to certain “piggyback” registration rights allowing the holders to include their shares in such registration, subject to certain marketing and other limitations set forth in the registration rights agreement.

The registration rights described above apply to (i) shares of our common stock held by our Principal Stockholders and their respective affiliates, and (ii) any of our capital stock (or that of our subsidiaries) issued or issuable with respect to the common stock described in clause (i) with respect to any dividend, distribution, recapitalization, reorganization, or certain other corporate transactions, or Registrable Securities. These registration rights are also for the benefit of any subsequent holder of Registrable Securities; provided that any particular securities will cease to be Registrable Securities when they have been sold in a registered public offering, sold in compliance with Rule 144 of the Securities Act or repurchased by us or our subsidiaries. In addition, with the consent of the company and holders of a majority of Registrable Securities, any Registrable Securities held by a person other than Silver Lake Sumeru and its affiliates will cease to be Registrable Securities if they can be sold without limitation under Rule 144 of the Securities Act.

Stock Subscription Agreement

On October 21, 2014, we entered into a stock subscription agreement with Iconiq pursuant to which we issued 357,142 shares of our common stock to Iconiq at $14.00 per share, for aggregate gross cash proceeds of $5,000,000.

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Legal Services Reimbursement

As of December 31, 2015, we accrued for costs of third party legal services incurred on behalf of Silver Lake Sumeru, Iconiq and Mr. Spanicciati relating to our initial public offering and other corporate related matters. Total amounts accrued at December 31, 2015 were $161,000, of which $84,000 were expensed during 2015 and $77,000 were included in other assets as deferred offering costs.

Employment Arrangement

Isaac Tucker, who is the son of Ms. Tucker, our Chief Executive Officer, has been employed by us since 2006 and currently serves as Chief Product Officer. His 2014, 2015 and 2016 total compensation, which is comprised of a base salary, bonus, equity and commissions, as applicable, was $424,436, $282,920 and $243,408, respectively, and was in line with similar roles at the company. In October 2016, we granted to Mr. Tucker an option award covering 20,000 shares of our common stock at an exercise price of $14.00 per share. Effective December 1, 2017, Mr. Tucker’s base salary was $300,000 per year with a 40% bonus target.

Participation in our Initial Public Offering

Certain entities affiliated with Iconiq, a holder of more than 5% of our common stock and an affiliate of a member of our board of directors, purchased 825,000 shares of our common stock in our initial public offering at the initial public offering price. The underwriters received the same discount from the shares sold to such affiliates as they did from all other shares sold to the public in the offering.

Certain Relationships

Mr. Spanicciati is our Chief Marketing Officer and a member of our board of directors.

Mr. Griffith is a member of our board of directors and a general partner of Iconiq.

From time to time, we do business with other companies affiliated with Silver Lake Sumeru and Iconiq. We believe that all such arrangements have been entered into in the ordinary course of business and have been conducted on an arms-length basis.

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UNDERWRITING

Under the terms and subject to the conditions in an underwriting agreement dated the date of this prospectus supplement, the underwriters named below, have severally agreed to purchase, and the selling stockholders have agreed to sell to them, severally, the number of shares indicated below at a price of $34.07 per share, which will result in approximately $153,315,000 of aggregate proceeds to the selling stockholders, before expenses.

The underwriters have an option to buy up to an additional 675,000 shares from the selling stockholders to cover sales by the underwriters of a greater number of shares than the total number set forth in the table above. They may exercise that option for 30 days from the date of this prospectus supplement. If any shares are purchased pursuant to this option, the underwriters will severally purchase shares in approximately the same proportion as set forth in the table above.

The underwriters are collectively referred to as the “underwriters”. To the extent there is one underwriter, “underwriters” refers to the underwriter listed in the table above. The underwriters are offering the shares of common stock subject to their acceptance of the shares from the selling stockholders and subject to prior sale. The underwriting agreement provides that the obligations of the several underwriters to pay for and accept delivery of the shares of common stock offered by this prospectus supplement are subject to the approval of certain legal matters by their counsel and to certain other conditions. The underwriters are obligated to take and pay for all of the shares of common stock offered by this prospectus supplement if any such shares are taken.

The underwriters propose to offer the shares of common stock for sale from time to time in one or more transactions on the Nasdaq Global Select Market, in the over-the-counter market, through negotiated transactions or otherwise at market prices prevailing at the time of sale, at prices related to prevailing market prices or at negotiated prices, subject to receipt and acceptance by it and subject to its right to reject any order in whole or in part. The underwriters may effect such transactions by selling the shares of common stock to or through dealers, and such dealers may receive compensation in the form of discounts, concessions or commissions from the underwriter and/or purchasers of shares of common stock for whom they act as agents or to whom they sell as principals. The underwriters may receive from purchasers of the shares nominal brokerage commissions in amounts agreed with the purchasers. The difference between the price at which the underwriter purchases shares of common stock and the price at which the underwriter resells such shares of common stock may be deemed underwriting compensation.

The estimated offering expenses payable by us are approximately $750,000. We have agreed to reimburse the underwriters for certain expenses incurred in connection with this offering in an amount up to $20,000.

Our common stock is listed on the NASDAQ Global Select Market under the symbol “BL.”

The company and its officers, directors, Principal Stockholders and the selling stockholders have agreed with the underwriters, subject to certain exceptions, not to dispose of or hedge any of their common stock or securities convertible into or exchangeable for shares of common stock during the period from the date of this prospectus supplement continuing through the date 60 days from the date the underwriters deliver the shares of common stock to purchasers, except with the prior written consent of the underwriters.

In order to facilitate the offering of the common stock, the underwriters may engage in transactions that stabilize, maintain or otherwise affect the price of the common stock. Specifically, the underwriters may sell

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more shares than they are obligated to purchase under the underwriting agreement, creating a short position. The underwriters can close out a short sale by either exercising their option to purchase additional shares or purchasing shares in the open market. As an additional means of facilitating this offering, the underwriters may bid for, and purchase, shares of common stock in the open market to stabilize the price of the common stock. These activities may raise or maintain the market price of the common stock above independent market levels or prevent or retard a decline in the market price of the common stock. The underwriters are not required to engage in these activities and may end any of these activities at any time.

We, the selling stockholders and the underwriters have agreed to indemnify each other against certain liabilities, including liabilities under the Securities Act.

A prospectus supplement in electronic format may be made available on websites maintained by one or more underwriters, or selling group members, if any, participating in this offering. The underwriters may agree to allocate a number of shares of common stock for sale to their online brokerage account holders. Allocations for internet distributions will be made to underwriters on the same basis as other allocations.

Other Relationships

The underwriters and their respective affiliates are full service financial institutions engaged in various activities, which may include sales and trading, commercial and investment banking, advisory, investment management, investment research, principal investment, hedging, market making, brokerage and other financial and non-financial activities and services. Certain of the underwriters and their respective affiliates have provided, and may in the future provide, a variety of these services to the issuer and to persons and entities with relationships with the issuer, for which they received or will receive customary fees and expenses.

In the ordinary course of their various business activities, the underwriters and their respective affiliates, officers, directors and employees may purchase, sell or hold a broad array of investments and actively trade securities, derivatives, loans, commodities, currencies, credit default swaps and other financial instruments for their own account and for the accounts of their customers, and such investment and trading activities may involve or relate to assets, securities and/or instruments of the issuer (directly, as collateral securing other obligations or otherwise) and/or persons and entities with relationships with the issuer. The underwriters and their respective affiliates may also communicate independent investment recommendations, market color or trading ideas and/or publish or express independent research views in respect of such assets, securities or instruments and may at any time hold, or recommend to clients that they should acquire, long and/or short positions in such assets, securities and instruments.

Selling Restrictions

European Economic Area

In relation to each Member State of the European Economic Area which has implemented the Prospectus Directive (each, a Relevant Member State), each underwriter has represented and agreed that with effect from and including the date on which the Prospectus Directive is implemented in that Relevant Member State (the Relevant Implementation Date) it has not made and will not make an offer of shares to the public in that Relevant Member State prior to the publication of a prospectus in relation to the shares which has been approved by the competent authority in that Relevant Member State or, where appropriate, approved in another Relevant Member State and notified to the competent authority in that Relevant Member State, all in accordance with the Prospectus Directive, except that it may, with effect from and including the Relevant Implementation Date, make an offer of shares to the public in that Relevant Member State at any time:

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For the purposes of this provision, the expression an “offer of shares to the public” in relation to any shares in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the shares to be offered so as to enable an investor to decide to purchase or subscribe the shares, as the same may be varied in that Relevant Member State by any measure implementing the Prospectus Directive in that Relevant Member State and the expression Prospectus Directive means Directive 2003/71/EC and includes any relevant implementing measure in each Relevant Member State.

Each underwriter has represented and agreed that:

Hong Kong

The shares may not be offered or sold by means of any document other than (i) in circumstances which do not constitute an offer to the public within the meaning of the Companies Ordinance (Cap.32, Laws of Hong Kong), or (ii) to “professional investors” within the meaning of the Securities and Futures Ordinance (Cap.571, Laws of Hong Kong) and any rules made thereunder, or (iii) in other circumstances which do not result in the document being a “prospectus” within the meaning of the Companies Ordinance (Cap.32, Laws of Hong Kong), and no advertisement, invitation or document relating to the shares may be issued or may be in the possession of any person for the purpose of issue (in each case whether in Hong Kong or elsewhere), which is directed at, or the contents of which are likely to be accessed or read by, the public in Hong Kong (except if permitted to do so under the laws of Hong Kong) other than with respect to shares which are or are intended to be disposed of only to persons outside Hong Kong or only to “professional investors” within the meaning of the Securities and Futures Ordinance (Cap. 571, Laws of Hong Kong) and any rules made thereunder.

Singapore

This prospectus supplement has not been registered as a prospectus with the Monetary Authority of Singapore. Accordingly, this prospectus supplement and any other document or material in connection with the offer or sale, or invitation for subscription or purchase, of the shares may not be circulated or distributed, nor may the shares be offered or sold, or be made the subject of an invitation for subscription or purchase, whether directly or indirectly, to persons in Singapore other than (i) to an institutional investor under Section 274 of the Securities and Futures Act, Chapter 289 of Singapore (the “SFA”), (ii) to a relevant person, or any person pursuant to Section 275(1A), and in accordance with the conditions, specified in Section 275 of the SFA or (iii) otherwise pursuant to, and in accordance with the conditions of, any other applicable provision of the SFA.

Where the shares are subscribed or purchased under Section 275 by a relevant person which is: (a) a corporation (which is not an accredited investor) the sole business of which is to hold investments and the entire

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share capital of which is owned by one or more individuals, each of whom is an accredited investor; or (b) a trust (where the trustee is not an accredited investor) whose sole purpose is to hold investments and each beneficiary is an accredited investor, shares, debentures and units of shares and debentures of that corporation or the beneficiaries’ rights and interest in that trust shall not be transferable for 6 months after that corporation or that trust has acquired the shares under Section 275 except: (1) to an institutional investor under Section 274 of the SFA or to a relevant person, or any person pursuant to Section 275(1A), and in accordance with the conditions, specified in Section 275 of the SFA; (2) where no consideration is given for the transfer; or (3) by operation of law.

Japan

The shares have not been and will not be registered under the Financial Instruments and Exchange Law of Japan (the Financial Instruments and Exchange Law) and each underwriter has agreed that it will not offer or sell any shares, directly or indirectly, in Japan or to, or for the benefit of, any resident of Japan (which term as used herein means any person resident in Japan, including any corporation or other entity organized under the laws of Japan), or to others for re-offering or resale, directly or indirectly, in Japan or to a resident of Japan, except pursuant to an exemption from the registration requirements of, and otherwise in compliance with, the Financial Instruments and Exchange Law and any other applicable laws, regulations and ministerial guidelines of Japan.

Canada

The shares may be sold in Canada only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the shares must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus supplement (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 of National Instrument 33-105 Underwriting Conflicts (NI 33-105), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

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LEGAL MATTERS

The validity of the shares of common stock offered hereby will be passed upon for us by Wilson Sonsini Goodrich & Rosati, P.C., Palo Alto, California. Wilson Sonsini Goodrich & Rosati, P.C. and certain of its members are associated with WS Investment Company, LLC (2007A), which is an investor in certain investment funds affiliated with Silver Lake Sumeru and directly or indirectly owns less than 0.1% of the outstanding shares of our common stock. Certain legal matters in connection with this offering will be passed upon by Latham & Watkins LLP, Los Angeles, California.

EXPERTS

The financial statements incorporated in this prospectus supplement by reference to the Annual Report on Form 10-K for the year ended December 31, 2016 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

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WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC a registration statement on Form S-3 under the Securities Act with respect to the securities described in this prospectus supplement. This prospectus supplement, which constitutes a part of the registration statement, does not contain all of the information set forth in the registration statement, some of which is contained in exhibits to the registration statement as permitted by the rules and regulations of the SEC. For further information with respect to us and our securities, we refer you to the registration statement, including the exhibits filed as a part of the registration statement. Statements contained in this prospectus supplement concerning the contents of any contract or any other document are not necessarily complete. If a contract or document has been filed as an exhibit to the registration statement, please see the copy of the contract or document that has been filed. A copy of the registration statement and the exhibits filed therewith may be inspected without charge at the public reference room maintained by the SEC, located at 100 F Street, N.E., Room 1580, Washington, D.C. 20549, and copies of all or any part of the registration statement may be obtained from that office at prescribed rates. You may obtain information on the operation of the SEC’s public reference room by calling the SEC at 1-800-SEC-0330. The SEC also maintains an Internet website that contains reports, proxy statements and other information about issuers that file electronically with the SEC. The address of that website is www.sec.gov.

We are subject to the information and periodic reporting requirements of the Exchange Act and, in accordance therewith, file periodic reports, proxy statements and other information with the SEC. These periodic reports, proxy statements and other information will be available for inspection and copying at the SEC’s public reference room and accessible through the SEC’s Internet website referenced above. We also maintain an Internet website at www.blackline.com, at which you may access these materials free of charge as soon as reasonably practicable after they are electronically filed with, or furnished to, the SEC. Information contained on, or that can be accessed through, our website does not constitute a part of this prospectus supplement or the registration statement of which this prospectus supplement forms a part, and is not incorporated by reference herein or therein. We have included our website address in this prospectus supplement solely for informational purposes and you should not consider any information contained on, or that can be accessed through, our website as part of this prospectus supplement or in deciding whether to purchase our securities.

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INFORMATION INCORPORATED BY REFERENCE

We “incorporate by reference” certain documents we file with the SEC, which means that we are disclosing important information to you by referring you to those documents. The information incorporated by reference is an important part of this prospectus supplement, and any information contained in this prospectus supplement or in any document incorporated by reference in this prospectus supplement will be deemed to be modified or superseded to the extent that a statement contained in this prospectus supplement or free writing prospectus provided to you in connection with this offering, or in any other document we subsequently file with the SEC that also is incorporated by reference in this prospectus supplement, modifies or supersedes the original statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to be a part of this prospectus supplement.

The following documents filed with the SEC are hereby incorporated by reference in this prospectus supplement:

All reports and other documents subsequently filed by us pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act after the date of this prospectus supplement and prior to the termination of this offering shall be deemed to be incorporated by reference in this prospectus supplement and to be part hereof from the date of filing of such reports and other documents.

Notwithstanding the statements in the preceding paragraphs, no document, report or exhibit (or portion of any of the foregoing) or any other information that we have “furnished” or may in the future “furnish” to the SEC pursuant to the Exchange Act shall be incorporated by reference into this prospectus supplement.

We hereby undertake to provide without charge to each person, including any beneficial owner, to whom a copy of this prospectus supplement is delivered, upon written or oral request of any such person, a copy of any and all of the information that has been or may be incorporated by reference in this prospectus supplement, other than exhibits to such documents, unless such exhibits have been specifically incorporated by reference thereto. Requests for such copies should be directed to our Investor Relations department, at the following address: BlackLine, Inc., 21300 Victory Boulevard, 12th Floor, Woodland Hills, California 91367, Attention: Investor Relations, or you may call us at (818) 223-9008.

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PROSPECTUS

$100,000,000

Common Stock

Preferred Stock

Depositary Shares

Debt Securities

Warrants

Subscription Rights

Units

33,738,329 Shares of Our Common Stock Offered by the Selling Stockholders

We may from time to time in one or more offerings offer and sell up to an aggregate amount of $100,000,000 common stock, preferred stock, depositary shares, debt securities, warrants to purchase common stock or preferred stock or debt securities, subscription rights or units in any combination of the foregoing.

In addition, the selling stockholders may from time to time offer and sell up to 33,738,329 shares of our common stock. We will not receive any of the proceeds from the sale of shares of our common stock by the selling stockholders.

Our common stock is listed on the NASDAQ Global Select Market under the symbol “BL”. On November 9, 2017, the reported closing sale price of our common stock on the NASDAQ Global Select Market was $35.28 per share.

The preferred stock, depositary shares, debt securities, warrants, subscription rights and units described in this prospectus have not been approved for listing on any market or exchange, and we have not made any application for such listing.

This prospectus describes the general terms of the securities we may offer and the general manner in which we may offer these securities. Each time we sell securities described herein, and in certain cases where one or more selling stockholders sell securities pursuant to this prospectus, we or the selling stockholders, as applicable, will provide prospective investors with a supplement to this prospectus that will contain specific information about the terms of that offering, including the specific amounts, prices and terms of the securities offered. Such prospectus supplements may also add, update or change information contained in this prospectus. The applicable prospectus supplement will contain information, where applicable, as to any other listing on the NASDAQ Global Select Market or any other securities market or other exchange with respect to the securities covered by such prospectus supplement. You should carefully read this prospectus and any applicable prospectus supplement, together with the documents we incorporate by reference, before you invest.

We are an “emerging growth company” as defined under the federal securities laws, and, as such, may elect to comply with certain reduced public company reporting requirements for this and future filings.

Investing in our securities involves risks. Please carefully read the information under the headings “Risk Factors” beginning on page 6 of this prospectus and “Item 1A—Risk Factors” of our most recent report on Form 10-K or 10-Q that is incorporated by reference in this prospectus before you invest in our securities.

Neither the Securities and Exchange Commission nor any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a criminal offense.

These securities may be offered and sold to or through one or more underwriters, dealers and agents, or directly to purchasers, on a continuous or delayed basis. If underwriters, dealers, or agents are used to sell the securities, we will name them and describe their compensation in a prospectus supplement. In addition, the underwriters may overallot a portion of the securities.

Prospectus dated November 17, 2017.

TABLE OF CONTENTS

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ABOUT THIS PROSPECTUS

This prospectus relates to the offer and the sale of any combination of the securities described in this prospectus for an aggregate offering of up to $100,000,000. This prospectus also relates to the offer and the sale of up to 33,738,329 of our shares of common stock by the selling stockholders identified in this prospectus. We will not receive any of the proceeds from the sale of shares of our common stock by the selling stockholders.

This prospectus is part of a registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or the SEC, using a “shelf” registration process. Under this shelf process, we may, from time to time, offer or sell any combination of the securities described in this prospectus in one or more offerings. In addition, under this shelf process, the selling stockholders may, from time to time, offer and sell up to an aggregate of 33,738,329 shares of our common stock in one or more offerings.

This prospectus provides you with a general description of the securities that we may offer. Each time we sell securities described herein, and in certain cases where one or more selling stockholders sell securities pursuant to this prospectus, we or the selling stockholders, as applicable, will provide prospective investors with a supplement to this prospectus that will contain specific information about the terms of that offering, including the specific amounts, prices and terms of the securities offered. The prospectus supplement may also add to, update or change information contained in this prospectus and, accordingly, to the extent inconsistent, information in this prospectus is superseded by the information in the prospectus supplement. You should carefully read both this prospectus and any accompanying prospectus supplement, together with the information incorporated by reference and any other offering materials. See “Where You Can Find More Information” and “Information Incorporated by Reference.”

You should only rely on the information contained or incorporated by reference in this prospectus and any prospectus supplement or free writing prospectus relating to a particular offering. No person has been authorized to give any information or make any representations in connection with this offering other than those contained or incorporated by reference in this prospectus, any accompanying prospectus supplement and any related free writing prospectus in connection with the offering described herein and therein. Neither this prospectus nor any prospectus supplement nor any related free writing prospectus shall constitute an offer to sell or a solicitation of an offer to buy offered securities in any jurisdiction in which it is unlawful for such person to make such an offering or solicitation. This prospectus does not contain all of the information included in the registration statement. For a more complete understanding of the offering of the securities, you should refer to the registration statement, including its exhibits.

You should read the entire prospectus and any prospectus supplement and any related free writing prospectus, as well as the documents incorporated by reference into this prospectus or any prospectus supplement or any related free writing prospectus, before making an investment decision. Neither the delivery of this prospectus or any prospectus supplement or any free writing prospectus nor any sale made hereunder shall under any circumstances imply that the information contained or incorporated by reference herein or in any prospectus supplement or free writing prospectus is correct as of any date subsequent to the date hereof or of such prospectus supplement or free writing prospectus, as applicable. You should assume that the information appearing in this prospectus, any prospectus supplement or any document incorporated by reference is accurate only as of the date of the applicable documents, regardless of the time of delivery of this prospectus or any sale of securities. Our business, financial condition, results of operations and prospects may have changed since that date.

For investors outside the United States: Neither us nor the selling stockholders have done anything that would permit our public offering or possession or distribution of this prospectus in any jurisdiction where action for that purpose is required, other than in the United States. Persons outside the United States who come into possession of this prospectus must inform themselves about, and observe any restrictions relating to, the offering of the securities and the distribution of this prospectus outside of the United States.

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RISK FACTORS

An investment in our securities involves a high degree of risk. Prior to making a decision about investing in our securities, you should carefully consider the risks, uncertainties and assumptions discussed under “Part I—Item 1A—Risk Factors” in our most recent Annual Report on Form 10-K or under “Part II—Item 1A—Risk Factors” in our Quarterly Reports on Form 10-Q and in other documents, which are incorporated herein by reference into this prospectus, and may be amended, supplemented or superseded from time to time by other reports we file with the SEC in the future, as well as the risk factors and other information contained in or incorporated by reference into any accompanying prospectus supplement. The risks and uncertainties we have described are not the only ones we face. Additional risks and uncertainties not presently known to us or that we currently deem immaterial may also affect our operations.

For more information about our SEC filings, please see “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”

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CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus includes and incorporates by reference forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, which statements involve substantial risk and uncertainties. In some cases, you can identify forward-looking statements by terminology such as “may,” “will,” “should,” “could,” “expect,” “plan,” “anticipate,” “believe,” “estimate,” “predict,” “intend,” “potential,” “would,” “continue,” “ongoing” or the negative of these terms or other comparable terminology. All statements other than statements of historical fact are statements that could be deemed forward-looking statements, including, but not limited to, statements regarding future financial and operational performance; statements concerning growth strategies including extension of distribution channels and strategic relationships, product innovation, international expansion, customer growth and expansion, customer service initiatives, expectations regarding deal size and increased focus on strategic products, expectations for hiring new talent and expanding our sales organization; our ability to accurately forecast revenue and appropriately plan expenses and investments; the demand for and benefits from the use of our current and future solutions; market acceptance of our solutions; and changes in the competitive environment in our industry and the markets in which we operate. These statements are based upon our historical performance and our current plans, estimates and expectations and are not a representation that such plans, estimates, or expectations will be achieved. Forward-looking statements are based on information available at the time those statements are made and/or management’s good faith beliefs and assumptions as of that time with respect to future events, and are subject to risks and uncertainties. If any of these risks or uncertainties materialize or if any assumptions prove incorrect, actual performance or results may differ materially from those expressed in or suggested by the forward looking statements. Readers are cautioned that these forward-looking statements are only predictions and are subject to risks, uncertainties, and assumptions that are difficult to predict, including those identified in the section in this prospectus entitled “Risk Factors,” in “Part I—Item 1A—Risk Factors” of our most recent Annual Report on Form 10-K or “Part II—Item 1A—Risk Factors” in our Quarterly Reports on Form 10-Q which are incorporated by reference in this prospectus as well as other disclosures included in this prospectus or any prospectus supplement hereto. Forward-looking statements should not be read as a guarantee of future performance or results, and you should not place undue reliance on such statements. Furthermore, we undertake no obligation to revise or update any forward-looking statements for any reason.

This prospectus and the documents incorporated by reference in this prospectus may contain market data that we obtain from industry sources. These sources do not guarantee the accuracy or completeness of the information. Although we believe that our industry sources are reliable, we do not independently verify the information. The market data may include projections that are based on a number of other projections. While we believe these assumptions to be reasonable and sound as of the date of this prospectus, actual results may differ from the projections.

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RATIO OF EARNINGS TO FIXED CHARGES

The following table sets forth our consolidated ratio of earnings to fixed charges for the periods indicated.

As of the date of this prospectus, we have no shares of preferred stock outstanding, and consequently, our ratio of earnings to combined fixed charges and preferred share dividends and ratio of earnings to fixed charges would be identical.

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USE OF PROCEEDS

Unless otherwise set forth in a prospectus supplement, we currently intend to use the net proceeds of any offering of securities for working capital and other general corporate purposes. Accordingly, we will have significant discretion in the use of any net proceeds. The specific allocations of the proceeds we receive from the sale of our securities will be described in the applicable prospectus supplement.

We will not receive any proceeds from the sale of shares of our common stock by the selling stockholders.

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DIVIDEND POLICY

We have never declared or paid, any cash dividends on our common stock. We currently intend to retain all of our future earnings, if any, to finance our operations and do not anticipate paying any cash dividends on our common stock in the foreseeable future. Any future determination as to the declaration and payment of dividends will be at the discretion of our board of directors and will depend on then-existing conditions, including our financial condition, operating results, contractual restrictions, capital requirements, business prospects, and other factors our board of directors may deem relevant.

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DESCRIPTION OF CAPITAL STOCK

The following description summarizes the material terms of our capital stock. Because it is only a summary, it does not contain all the information that may be important to you. For a complete description of our capital stock, you should refer to our amended and restated certificate of incorporation and our amended and restated bylaws and to the provisions of applicable Delaware law.

Our authorized capital stock consists of 500,000,000 shares of common stock, $0.01 par value and 50,000,000 shares of preferred stock, $0.01 par value. As of November 6, 2017, there were 52,860,792 shares of our common stock issued and outstanding held of record by 29 stockholders.

Common Stock

Voting Rights

Each holder of our common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders, including the election of directors. Under our amended and restated certificate of incorporation and bylaws, our stockholders will not have cumulative voting rights. Because of this, the holders of a majority of the shares of common stock entitled to vote in any election of directors can elect all of the directors standing for election, if they should so choose.

Dividends

Holders of common stock are entitled to receive ratably those dividends, if any, as may be declared from time to time by the board of directors out of legally available funds.

Liquidation

In the event of our liquidation, dissolution or winding up, holders of common stock will be entitled to share ratably in the net assets legally available for distribution to stockholders after the payment of all of our debts and other liabilities.

Rights and Preferences

Holders of shares of common stock have no preemptive, conversion or subscription rights and there are no redemption or sinking fund provisions applicable to the common stock. The rights, preferences and privileges of the holders of shares of common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock that we may designate in the future.

Preferred Stock

No shares of our preferred stock are currently outstanding. Under our amended and restated certificate of incorporation, our board of directors, without further action by our stockholders, is authorized to issue shares of preferred stock in one or more classes or series. The board may fix or alter the rights, preferences and privileges of the preferred stock, along with any limitations or restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences of each class or series of preferred stock. The preferred stock could have voting or conversion rights that could adversely affect the voting power or other rights of holders of our common stock. The issuance of preferred stock could also have the effect, under certain circumstances, of delaying, deferring or preventing a change of control of our company. We currently have no plans to issue any shares of preferred stock.

Anti-Takeover Effects of Delaware Law and Our Certificate of Incorporation and Bylaws

Our amended and restated certificate of incorporation and our amended and restated bylaws contain certain provisions that could have the effect of delaying, deferring or discouraging another party from acquiring control

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of us. These provisions are also designed, in part, to encourage persons seeking to acquire control of us to negotiate first with our board of directors. We believe that the benefits of increased protection of our potential ability to negotiate more favorable terms with an unfriendly or unsolicited acquirer outweigh the disadvantages of discouraging a proposal to acquire us.

Classified Board

Our amended and restated certificate of incorporation provides that our board of directors is divided into three classes of directors, with the classes as nearly equal in number as possible, and with the directors serving three-year terms. As a result, approximately one-third of our board will be elected each year. The classification of directors will have the effect of making it more difficult for stockholders to change the composition of our board. Our amended and restated certificate of incorporation also provides that, subject to any rights of holders of preferred stock to elect additional directors under specified circumstances and the Stockholders’ Agreement by and between the Company and our Principal Stockholders, dated as of October 27, 2016, or the Stockholders’ Agreement, the number of directors will be fixed exclusively pursuant to a resolution adopted by our board. Our board of directors is currently comprised of nine members.

Stockholder Action by Written Consent

Our amended and restated certificate of incorporation precludes stockholder action by written consent at any time when the Principal Stockholders beneficially own, in the aggregate, less than 35% of the total number of shares of our common stock then outstanding.

Special Meetings of Stockholders

Our amended and restated certificate of incorporation provides that, except as required by law, special meetings of our stockholders may be called at any time only by or at the direction of our board or the chairman of our board; provided, however, at any time when the Principal Stockholders own, in the aggregate, at least 35% in voting power of our stock entitled to vote generally in the election of directors, special meetings of our stockholders will also be called by our board or the chairman of our board at the request of Silver Lake Sumeru or Ms. Tucker. Our amended and restated bylaws prohibit the conduct of any business at a special meeting other than as specified in the notice for such meeting. These provisions may have the effect of deferring, delaying or discouraging hostile takeovers, or changes in control or management of the company.

Advance Notice Procedures

Our amended and restated bylaws contain an advance notice procedure for stockholder proposals to be brought before an annual meeting of our stockholders, including proposed nominations of persons for election to our board; provided, however, such advance notice procedures will not apply to a Principal Stockholder at any time when such Principal Stockholder beneficially owns at least 10% of the total number of shares of our common stock then outstanding. Stockholders at an annual meeting will only be able to consider proposals or nominations specified in the notice of meeting or brought before the meeting by or at the direction of our board or by a stockholder who was a stockholder of record on the record date for the meeting, who is entitled to vote at the meeting and who has given our secretary timely written notice, in proper form, of the stockholder’s intention to bring that business before the meeting. Although the amended and restated bylaws will not give our board the power to approve or disapprove stockholder nominations of candidates or proposals regarding other business to be conducted at a special or annual meeting, the bylaws may have the effect of precluding the conduct of certain business at a meeting if the proper procedures are not followed or may discourage or deter a potential acquirer from conducting a solicitation of proxies to elect its own slate of directors or otherwise attempting to obtain control of the company.

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Removal of Directors; Vacancies

Our amended and restated certificate of incorporation provides that directors may be removed with or without cause upon the affirmative vote of a majority in voting power of all outstanding shares of stock entitled to vote thereon, voting together as a single class; provided, however, at any time when the Principal Stockholders beneficially own, in the aggregate, less than 40% of the voting power of our stock entitled to vote generally in the election of directors, directors may only be removed for cause, and only by the affirmative vote of holders of at least 66 2/3% in voting power of our stock entitled to vote thereon, voting together as a single class. In connection with votes for removal, the parties to the Stockholders’ Agreement will agree to vote their shares in accordance with the board composition requirements in such agreement and the wishes of the party which designated a director regarding removal of such director. Any newly created directorships that result in a vacancy on the board will be filled by Silver Lake Sumeru if Silver Lake Sumeru is entitled to fill the vacancy pursuant to the Stockholders’ Agreement. In the event that Silver Lake Sumeru is not entitled to, or chooses not to, fill the vacancy, then such vacancy may only be filled by a majority of the directors then in office, even if less than a quorum, or by a sole remaining director (and not by the stockholders). In addition, in the event that Ms. Tucker or Mr. Spanicciati ceases to be employed by the company for any reason and she or he beneficially owns less than 5% of the total number of shares of our common stock outstanding, (i) she or he will be required to immediately tender her or his resignation from the board of directors effective only upon acceptance by the board of directors and (ii) the board of directors may, in its sole discretion, accept or reject such resignation. If the board of directors rejects the resignation, Ms. Tucker or Mr. Spanicciati, as applicable, will continue to have the right to be designated for membership on the board of directors; provided that the board of directors will have the right, by unanimous vote of the other directors (excluding both Ms. Tucker and Mr. Spanicciati), to require such director’s resignation from the board of directors if the board of directors determines such resignation would be in the best interests of the company, regardless of the number of shares of common stock held by Ms. Tucker or Mr. Spanicciati.

Supermajority Approval Requirements

Our amended and restated certificate of incorporation and amended and restated bylaws provide that our board of directors is expressly authorized to make, alter, amend and rescind, in whole or in part, our bylaws without a stockholder vote in any matter not inconsistent with the laws of the State of Delaware and our certificate of incorporation. For as long as the Principal Stockholders beneficially own, in the aggregate, at least 40% in voting power of our stock entitled to vote generally in the election of directors, any amendment, alteration, rescission or repeal of our amended and restated bylaws by our stockholders will require the affirmative vote of 60% of the voting power of all the then outstanding shares of our stock entitled to vote thereon, voting together as a single class. At any time when the Principal Stockholders beneficially own, in the aggregate, less than 40% in voting power of our stock entitled to vote generally in the election of directors, any amendment, alteration, rescission or repeal of our amended and restated bylaws by our stockholders will require the affirmative vote of the holders of at least 75% voting power of all the then outstanding shares of our stock entitled to vote thereon, voting together as a single class.

The DGCL provides generally that the affirmative vote of a majority of the outstanding shares entitled to vote thereon, voting together as a single class, is required to amend a corporation’s certificate of incorporation, unless the certificate of incorporation requires a greater percentage.

Our certificate of incorporation provides that (i) at any time when the Principal Stockholders collectively beneficially own, in the aggregate, at least 40% in voting power of our stock entitled to vote generally in the election of directors, the amended and restated certificate of incorporation may be amended, altered, repealed or rescinded only by the affirmative vote of the holders of at least 60% of the voting power of our stock entitled to vote thereon, voting together as a single class, and (ii) at any time when the Principal Stockholders beneficially own, in the aggregate, less than 40% in voting power of our stock entitled to vote generally in the election of directors, the following provisions in our amended and restated certificate of incorporation may be amended,

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altered, repealed or rescinded only by the affirmative vote of the holders of at least 75% of the voting power of all the then outstanding shares of our stock entitled to vote thereon, voting together as a single class:

The combination of the classification of our board of directors, the lack of cumulative voting and the supermajority voting requirements will make it more difficult for our existing stockholders to replace our board of directors as well as for another party to obtain control of us by replacing our board. Because our board of directors has the power to retain and discharge our officers, these provisions could also make it more difficult for existing stockholders or another party to effect a change in management.

Authorized but Unissued Shares

Our authorized but unissued shares of common stock and preferred stock are available for future issuance without stockholder approval, subject to stock exchange rules. These additional shares may be utilized for a variety of corporate purposes, including future public offerings to raise additional capital, corporate acquisitions and employee benefit plans. One of the effects of the existence of authorized but unissued common stock or preferred stock may be to enable our board to issue shares to persons friendly to current management, which issuance could render more difficult or discourage an attempt to obtain control of the company by means of a merger, tender offer, proxy contest or otherwise, and thereby protect the continuity of our management and possibly deprive our stockholders of opportunities to sell their shares of common stock at prices higher than prevailing market prices.

Business Combinations

We are not subject to the provisions of Section 203 of the Delaware General Corporation Law, or DGCL. In general, Section 203 prohibits a publicly held Delaware corporation from engaging in a “business combination” with an “interested stockholder” for a three-year period following the time that the person becomes an interested stockholder, unless the business combination is approved in a prescribed manner. A “business combination” includes, among other things, a merger, asset or stock sale or other transaction resulting in a financial benefit to the interested stockholder. An “interested stockholder” is a person who, together with affiliates and associates, owns, or did own within three years prior to the determination of interested stockholder status, 15% or more of the corporation’s voting stock.

Under Section 203, a business combination between a corporation and an interested stockholder is prohibited unless it satisfies one of the following conditions: (1) before the stockholder became an interested stockholder, the board of directors approved either the business combination or the transaction which resulted in the stockholder becoming an interested stockholder; (2) upon consummation of the transaction which resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting

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stock of the corporation outstanding at the time the transaction commenced, excluding for purposes of determining the voting stock outstanding, shares owned by persons who are directors and also officers, and employee stock plans, in some instances; or (3) at or after the time the stockholder became an interested stockholder, the business combination was approved by the board of directors and authorized at an annual or special meeting of the stockholders by the affirmative vote of at least two-thirds of the outstanding voting stock which is not owned by the interested stockholder.

A Delaware corporation may “opt out” of these provisions with an express provision in its original certificate of incorporation or an express provision in its certificate of incorporation or bylaws resulting from a stockholders’ amendment approved by at least a majority of the outstanding voting shares.

We have opted out of Section 203; however, our amended and restated certificate of incorporation contains similar provisions providing that we may not engage in certain “business combinations” with any “interested stockholder” for a three-year period following the time that the stockholder became an interested stockholder, unless:

Under certain circumstances, this provision will make it more difficult for a person who would be an “interested stockholder” to effect various business combinations with the company for a three-year period. This provision may encourage companies interested in acquiring the company to negotiate in advance with our board because the stockholder approval requirement would be avoided if our board approves either the business combination or the transaction which results in the stockholder becoming an interested stockholder. These provisions also may have the effect of preventing changes in our board and may make it more difficult to accomplish transactions which stockholders may otherwise deem to be in their best interests.

Our certificate of incorporation provides that Silver Lake Sumeru, Iconiq and Ms. Tucker, and certain transferees who, following the transfer, will beneficially own at least 15% of the total number of shares of our common stock then outstanding, and any of their respective affiliates or successors or any group as to which such persons are a party, do not constitute “interested stockholders” for purposes of this provision.

Exclusive Forum

Our amended and restated bylaws provides that, unless we consent in writing to the selection of an alternative forum, the sole and exclusive forum for (1) any derivative action or proceeding brought on our behalf, (2) any action asserting a claim of breach of a fiduciary duty owed by any of our directors, officers or other employees to us or our stockholders, (3) any action asserting a claim against the company or any director or officer of the company arising pursuant to any provision of the DGCL, or (4) any other action asserting a claim that is governed by the internal affairs doctrine shall be a state or federal court located within the State of Delaware, in all cases subject to the court’s having jurisdiction over indispensable parties named as defendants. Any person or entity purchasing or otherwise acquiring any interest in our shares of capital stock shall be deemed to have notice of and consented to this provision. Although we believe these provisions benefit us by providing increased consistency in the application of Delaware law for the specified types of actions and proceedings, the provisions may have the effect of discouraging lawsuits against us or our directors and officers.

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Conflicts of Interest

Delaware law permits corporations to adopt provisions renouncing any interest or expectancy in certain opportunities that are presented to the corporation or its officers, directors or stockholders. Our amended and restated certificate of incorporation, to the maximum extent permitted from time to time by Delaware law, renounces any interest or expectancy that we have in, or right to be offered an opportunity to participate in, specified business opportunities that are from time to time presented to certain of our officers, directors or stockholders or their respective affiliates, other than those officers, directors, stockholders or affiliates who are our or our subsidiaries’ employees. Our certificate of incorporation provides that, to the fullest extent permitted by law, none of Silver Lake Sumeru or Iconiq, their respective affiliates or the directors they designate will have any duty to refrain from (1) engaging in a corporate or business opportunity or offer a prospective economic or competitive advantage in which we, or any of our affiliates, directly could have an interest of expectancy, (2) otherwise competing with us or our affiliates, (3) otherwise doing business with any potential or actual customer or supplier of ours or our affiliates or (4) otherwise employing or engaging any officer or employee or any of our affiliates. In addition, to the fullest extent permitted by law, in the event that Silver Lake Sumeru or Iconiq, their respective affiliates or the directors they designate acquires knowledge of a potential transaction or other business opportunity which may be a corporate opportunity for itself, herself or himself or its or his affiliates or for us or our affiliates, such person will have no duty to communicate or offer such transaction or business opportunity to us or any of our affiliates and they may take any such opportunity for themselves or offer it to another person or entity. Our amended and restated certificate of incorporation does not renounce our interest in any business opportunity that is expressly offered to Silver Lake Sumeru, Iconiq, their respective affiliates or the directors they designate solely in his or her capacity as a director or officer of the company. To the fullest extent permitted by law, no business opportunity will be deemed to be a potential corporate opportunity for us unless we would be permitted to undertake the opportunity under our amended and restated certificate of incorporation, we have sufficient financial resources to undertake the opportunity, the opportunity would be in line with our business, and the opportunity is one in which we have an interest or reasonable expectancy.

Limitations on Liability and Indemnification of Officers and Directors

The DGCL authorizes corporations to limit or eliminate the personal liability of directors to corporations and their stockholders for monetary damages for breaches of directors’ fiduciary duties, subject to certain exceptions. Our amended and restated certificate of incorporation includes a provision that eliminates the personal liability of directors for monetary damages for any breach of fiduciary duty as a director, except to the extent such exemption from liability or limitation thereof is not permitted under the DGCL. These provisions eliminate the rights of us and our stockholders, through stockholders’ derivative suits on our behalf, to recover monetary damages from a director for breach of fiduciary duty as a director, including breaches resulting from grossly negligent behavior. However, exculpation will not apply to any director if the director has acted in bad faith, knowingly or intentionally violated the law, authorized illegal dividends or redemptions or derived an improper benefit from his or her actions as a director.

Our amended and restated bylaws provide that we must indemnify and advance expenses to our directors and officers to the fullest extent authorized by the DGCL. We also are expressly authorized to carry directors’ and officers’ liability insurance providing indemnification for our directors, officers and certain employees for some liabilities. We believe that these indemnification and advancement provisions and insurance will be useful to attract and retain qualified directors and officers.

The limitation of liability, indemnification and advancement provisions included in our certificate of incorporation and bylaws may discourage stockholders from bringing a lawsuit against directors for breaches of their fiduciary duty. These provisions also may have the effect of reducing the likelihood of derivative litigation against directors and officers, even though such an action, if successful, might otherwise benefit us and our stockholders. In addition, your investment may be adversely affected to the extent we pay the costs of settlement and damage awards against directors and officers pursuant to these indemnification provisions.

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There is currently no pending material litigation or proceeding involving any of our directors, officers or employees for which indemnification is sought.

Transfer Agent and Registrar

The transfer agent and registrar for our common stock is American Stock Transfer & Trust Company, LLC. The transfer agent and registrar’s address is 6201 15th Avenue, Brooklyn, New York 11219, and its telephone number is (718) 921-8206.

Listing

Our common stock is listed on the NASDAQ Global Select Market under the symbol “BL”.

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DESCRIPTION OF THE DEPOSITARY SHARES

General

At our option, we may elect to offer fractional shares of preferred stock, rather than full shares of preferred stock. If we do elect to offer fractional shares of preferred stock, we will issue receipts for depositary shares and each of these depositary shares will represent a fraction of a share of a particular series of preferred stock, as specified in the applicable prospectus supplement. Each owner of a depositary share will be entitled, in proportion to the applicable fractional interest in shares of preferred stock underlying that depositary share, to all rights and preferences of the preferred stock underlying that depositary share. These rights may include dividend, voting, redemption and liquidation rights.

The shares of preferred stock underlying the depositary shares will be deposited with a bank or trust company selected by us to act as depositary, under a deposit agreement by and among us, the depositary and the holders of the depositary receipts. The depositary will be the transfer agent, registrar and dividend disbursing agent for the depositary shares.

The depositary shares will be evidenced by depositary receipts issued pursuant to the depositary agreement. Holders of depositary receipts agree to be bound by the deposit agreement, which requires holders to take certain actions such as filing proof of residence and paying certain charges.

The summary of terms of the depositary shares contained in this prospectus is not complete, and is subject to modification in any prospectus supplement for any issuance of depositary shares. You should refer to the forms of the deposit agreement, our amended and restated certificate of incorporation and the certificate of designation that are, or will be, filed with the SEC for the applicable series of preferred stock.

Dividends

The depositary will distribute cash dividends or other cash distributions, if any, received in respect of the series of preferred stock underlying the depositary shares to the record holders of depositary receipts in proportion to the number of depositary shares owned by those holders on the relevant record date. The relevant record date for depositary shares will be the same date as the record date for the preferred stock.

In the event of a distribution other than in cash, the depositary will distribute property received by it to the record holders of depositary receipts that are entitled to receive the distribution, unless the depositary determines that it is not feasible to make the distribution. If this occurs, the depositary, with our approval, may adopt another method for the distribution, including selling the property and distributing the net proceeds to the holders.

Liquidation Preference

If a series of preferred stock underlying the depositary shares has a liquidation preference, in the event of our voluntary or involuntary liquidation, dissolution or winding up, holders of depositary shares will be entitled to receive the fraction of the liquidation preference accorded each share of the applicable series of preferred stock, as set forth in the applicable prospectus supplement.

Redemption

If a series of preferred stock underlying the depositary shares is subject to redemption, the depositary shares will be redeemed from the proceeds received by the depositary resulting from the redemption, in whole or in part, of the preferred stock held by the depositary. Whenever we redeem any preferred stock held by the depositary, the depositary will redeem, as of the same redemption date, the number of depositary shares representing the preferred stock so redeemed. The depositary will mail the notice of redemption to the record holders of the

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depositary receipts promptly upon receiving the notice from us and not fewer than 20 or more than 60 days, unless otherwise provided in the applicable prospectus supplement, prior to the date fixed for redemption of the preferred stock.

Voting

Upon receipt of notice of any meeting at which the holders of our preferred stock are entitled to vote, the depositary will mail the information contained in the notice of meeting to the record holders of the depositary receipts underlying the preferred stock. Each record holder of those depositary receipts on the record date will be entitled to instruct the depositary as to the exercise of the voting rights pertaining to the amount of preferred stock underlying that holder’s depositary shares. The record date for the depositary will be the same date as the record date for the preferred stock. The depositary will, to the extent practicable, vote the preferred stock underlying the depositary shares in accordance with these instructions. We will agree to take all action that may be deemed necessary by the depositary in order to enable the depositary to vote the preferred stock in accordance with these instructions. The depositary will not vote the preferred stock to the extent that it does not receive specific instructions from the holders of depositary receipts.

Withdrawal of Preferred Stock

Owners of depositary shares will be entitled to receive upon surrender of depositary receipts at the principal office of the depositary and payment of any unpaid amount due to the depositary, the number of whole shares of preferred stock underlying their depositary shares.

Partial shares of preferred stock will not be issued. Holders of our preferred stock will not be entitled to deposit the shares under the deposit agreement or to receive depositary receipts evidencing depositary shares for the preferred stock.

Amendment and Termination of the Deposit Agreement

The form of depositary receipt evidencing the depositary shares and any provision of the deposit agreement may be amended by agreement between the depositary and us. However, any amendment which materially and adversely alters the rights of the holders of depositary shares, other than fee changes, will not be effective unless the amendment has been approved by at least a majority of the outstanding depositary shares. The deposit agreement may be terminated by the depositary or us only if:

Charges of Depositary

We will pay all transfer and other taxes and governmental charges arising solely from the existence of the depositary arrangement. We will also pay charges of the depositary in connection with:

Holders of depositary receipts will pay transfer, income and other taxes and governmental charges and other specified charges as provided in the deposit agreement for their accounts. If these charges have not been paid, the depositary may:

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Miscellaneous

The depositary will forward to the holders of depositary receipts all reports and communications we deliver to the depositary that we are required to furnish to the holders of the preferred stock. In addition, the depositary will make available for inspection by holders of depositary receipts at the principal office of the depositary, and at such other places as it may from time to time deem advisable, any reports and communications we deliver to the depositary as the holder of preferred stock.

Neither the depositary nor we will be liable if either the depositary or we are prevented or delayed by law or any circumstance beyond the control of either the depositary or us in performing our respective obligations under the deposit agreement. Our obligations and the depositary’s obligations will be limited to the performance in good faith of our or the depositary’s respective duties under the deposit agreement. Neither the depositary nor we will be obligated to prosecute or defend any legal proceeding in respect of any depositary shares or preferred stock unless satisfactory indemnity is furnished. The depositary and we may rely on:

Resignation and Removal of Depositary

The depositary may resign at any time by delivering a notice to us. We may remove the depositary at any time. Any such resignation or removal will take effect upon the appointment of a successor depositary and its acceptance of such appointment. The successor depositary must be appointed within 60 days after delivery of the notice for resignation or removal. The successor depositary must be a bank and trust company having its principal office in the United States of America and having a combined capital and surplus of at least $50,000,000.

Federal Income Tax Consequences

Owners of the depositary shares will be treated for U.S. federal income tax purposes as if they were owners of the preferred stock underlying the depositary shares. As a result, owners will be entitled to take into account for U.S. federal income tax purposes and deductions to which they would be entitled if they were holders of such preferred stock. No gain or loss will be recognized for U.S. federal income tax purposes upon the withdrawal of preferred stock in exchange for depositary shares. The tax basis of each share of preferred stock to an exchanging owner of depositary shares will, upon such exchange, be the same as the aggregate tax basis of the depositary shares exchanged. The holding period for preferred stock in the hands of an exchanging owner of depositary shares will include the period during which such person owned such depositary shares.

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DESCRIPTION OF THE DEBT SECURITIES

The debt securities may be either secured or unsecured and will either be our senior debt securities or our subordinated debt securities. The debt securities will be issued under one or more separate indentures between us and a trustee to be specified in an accompanying prospectus supplement. Senior debt securities will be issued under a senior indenture and subordinated debt securities will be issued under a subordinated indenture. Together, the senior indenture and the subordinated indenture are called indentures in this description. This prospectus, together with the applicable prospectus supplement, will describe the terms of a particular series of debt securities.

The following is a summary of selected provisions and definitions of the indentures and debt securities to which any prospectus supplement may relate. The summary of selected provisions of the indentures and the debt securities appearing below is not complete and is subject to, and qualified entirely by reference to, all of the provisions of the applicable indenture and certificates or supplemental indenture evidencing the applicable debt securities. For additional information, you should look at the applicable indenture and the certificate or supplemental indenture evidencing the applicable debt security that is filed as an exhibit to the registration statement that includes the prospectus. In this description of the debt securities, the words “we,” “us,” or “our” refer only to BlackLine, Inc. and not to any of our subsidiaries, unless we expressly state or the context otherwise requires.

The following description sets forth selected general terms and provisions of the applicable indenture and debt securities to which any prospectus supplement may relate. Other specific terms of the applicable indenture and debt securities will be described in the applicable prospectus supplement. If any particular terms of the indenture or debt securities described in a prospectus supplement differ from any of the terms described below, then the terms described below will be deemed to have been superseded by that prospectus supplement.

General

Debt securities may be issued in separate series without limitation as to aggregate principal amount. We may specify a maximum aggregate principal amount for the debt securities of any series.

We are not limited as to the amount of debt securities we may issue under the indentures. Unless otherwise provided in a prospectus supplement, a series of debt securities may be reopened to issue additional debt securities of such series.

The prospectus supplement relating to a particular series of debt securities will set forth:

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Unless otherwise specified in the prospectus supplement, the debt securities will be registered debt securities. Debt securities may be sold at a substantial discount below their stated principal amount, bearing no interest or interest at a rate which at time of issuance is below market rates. The U.S. federal income tax considerations applicable to debt securities sold at a discount will be described in the applicable prospectus supplement.

Exchange and Transfer

Debt securities may be transferred or exchanged at the office of the security registrar or at the office of any transfer agent designated by us.

We will not impose a service charge for any transfer or exchange, but we may require holders to pay any tax or other governmental charges associated with any transfer or exchange.

In the event of any partial redemption of debt securities of any series, we will not be required to:

We will appoint the trustee as the initial security registrar. Any transfer agent, in addition to the security registrar initially designated by us, will be named in the prospectus supplement. We may designate additional transfer agents or change transfer agents or change the office of the transfer agent. However, we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

Global Securities

The debt securities of any series may be represented, in whole or in part, by one or more global securities. Each global security will:

No global security may be exchanged in whole or in part for debt securities registered in the name of any person other than the depositary or any nominee unless:

As long as the depositary, or its nominee, is the registered owner of a global security, the depositary or nominee will be considered the sole owner and holder of the debt securities represented by the global security for all

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purposes under the indentures. Except in the above limited circumstances, owners of beneficial interests in a global security will not be:

Payments on a global security will be made to the depositary or its nominee as the holder of the global security. Some jurisdictions have laws that require that certain purchasers of securities take physical delivery of such securities in definitive form. These laws may impair the ability to transfer beneficial interests in a global security.

Institutions that have accounts with the depositary or its nominee are referred to as “participants.” Ownership of beneficial interests in a global security will be limited to participants and to persons that may hold beneficial interests through participants. The depositary will credit, on its book-entry registration and transfer system, the respective principal amounts of debt securities represented by the global security to the accounts of its participants.

Ownership of beneficial interests in a global security will be shown on and effected through records maintained by the depositary, with respect to participants’ interests, or any participant, with respect to interests of persons held by participants on their behalf.

Payments, transfers and exchanges relating to beneficial interests in a global security will be subject to policies and procedures of the depositary. The depositary policies and procedures may change from time to time. Neither any trustee nor we will have any responsibility or liability for the depositary’s or any participant’s records with respect to beneficial interests in a global security.

Payment and Paying Agents

Unless otherwise indicated in a prospectus supplement, the provisions described in this paragraph will apply to the debt securities. Payment of interest on a debt security on any interest payment date will be made to the person in whose name the debt security is registered at the close of business on the regular record date. Payment on debt securities of a particular series will be payable at the office of a paying agent or paying agents designated by us. However, at our option, we may pay interest by mailing a check to the record holder. The trustee will be designated as our initial paying agent.

We may also name any other paying agents in a prospectus supplement. We may designate additional paying agents, change paying agents or change the office of any paying agent. However, we will be required to maintain a paying agent in each place of payment for the debt securities of a particular series.

All moneys paid by us to a paying agent for payment on any debt security that remain unclaimed for a period ending the earlier of:

will be repaid to us and, thereafter, the holder may look only to us for such payment.

No Protection in the Event of a Change of Control

Unless otherwise indicated in a prospectus supplement with respect to a particular series of debt securities, the debt securities will not contain any provisions that may afford holders of the debt securities protection in the event we have a change in control or in the event of a highly-leveraged transaction, whether or not such transaction results in a change in control.

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Covenants

Unless otherwise indicated in a prospectus supplement with respect to a particular series of debt securities, the debt securities will not contain any financial or restrictive covenants.

Consolidation, Merger and Sale of Assets

Unless we indicate otherwise in a prospectus supplement with respect to a particular series of debt securities, we may not consolidate with or merge into any other person (other than one of our subsidiaries), in a transaction in which we are not the surviving corporation, or convey, transfer or lease our properties and assets substantially as an entirety to, any person (other than to one or more subsidiaries of BlackLine, Inc.), unless:

Events of Default

Unless we indicate otherwise in a prospectus supplement, the following will be events of default for any series of debt securities under the indentures:

Additional or different events of default applicable to a series of debt securities may be described in a prospectus supplement. An event of default of one series of debt securities is not necessarily an event of default for any other series of debt securities.

The trustee may withhold notice to the holders of any default, except defaults in the payment of principal, premium, if any, interest, any sinking fund installment on, or with respect to any conversion right of, the debt securities of such series. However, the trustee must consider it to be in the interest of the holders of the debt securities of such series to withhold this notice.

Unless we indicate otherwise in a prospectus supplement, if an event of default, other than an event of default described in the fifth bullet point above with respect to us, shall occur and be continuing with respect to any series of debt securities, either the trustee or the holders of at least 25% in aggregate principal amount of the outstanding securities of that series may declare the principal amount and premium, if any, of the debt securities of that series, or if any debt securities of that series are original issue discount securities, such other amount as may be specified in the applicable prospectus supplement, in each case together with accrued and unpaid interest thereon, if any, to be due and payable immediately.

Unless we indicate otherwise in a prospectus supplement, if an event of default described in clause (5) above shall occur with respect to us, the principal amount and premium, if any, of all the debt securities of

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that series, or if any debt securities of that series are original issue discount securities, such other amount as may be specified in the applicable prospectus supplement, in each case together with accrued and unpaid interest thereon, if any, will automatically become immediately due and payable. Any payment by us on the subordinated debt securities following any such acceleration will be subject to the subordination provisions described below under “Subordinated Debt Securities.”

Notwithstanding the foregoing, each indenture will provide that we may, at our option, elect that the sole remedy for an event of default relating to our failure to comply with our obligations described under the section entitled “Reports” below or our failure to comply with the requirements of Section 314(a)(1) of the Trust Indenture Act will for the first 360 days after the occurrence of such an event of default consist exclusively of the right to receive additional interest on the relevant series of debt securities at an annual rate equal to (1) 0.25% of the principal amount of such series of debt securities for the first 180 days after the occurrence of such event of default and (2) 0.50% of the principal amount of such series of debt securities from the 181st day to, and including, the 360th day after the occurrence of such event of default, which we call “additional interest.” If we so elect, the additional interest will accrue on all outstanding debt securities from and including the date on which such event of default first occurs until such violation is cured or waived and shall be payable on each relevant interest payment date to holders of record on the regular record date immediately preceding the interest payment date. On the 361st day after such event of default (if such violation is not cured or waived prior to such 361st day), the debt securities will be subject to acceleration as provided above. In the event we do not elect to pay additional interest upon any such event of default in accordance with this paragraph, the debt securities will be subject to acceleration as provided above.

In order to elect to pay the additional interest as the sole remedy during the first 360 days after the occurrence of any event of default relating to the failure to comply with the reporting obligations in accordance with the preceding paragraph, we must notify all holders of debt securities and the trustee and paying agent of such election prior to the close of business on the first business day following the date on which such event of default occurs. Upon our failure to timely give such notice or pay the additional interest, the debt securities will be immediately subject to acceleration as provided above.

After acceleration, the holders of a majority in aggregate principal amount of the outstanding securities of that series may, under certain circumstances, rescind and annul such acceleration if all events of default, other than the non-payment of accelerated principal, or other specified amounts or interest, have been cured or waived.

Other than the duty to act with the required care during an event of default, the trustee will not be obligated to exercise any of its rights or powers at the request of the holders unless the holders shall have offered to the trustee reasonable indemnity. Generally, the holders of a majority in aggregate principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee.

A holder of debt securities of any series will not have any right to institute any proceeding under the indentures, or for the appointment of a receiver or a trustee, or for any other remedy under the indentures, unless:

(1) the holder has previously given to the trustee written notice of a continuing event of default with respect to the debt securities of that series;

(2) the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series have made a written request and have offered reasonable indemnity to the trustee to institute the proceeding; and

(3) the trustee has failed to institute the proceeding and has not received direction inconsistent with the original request from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series within 60 days after the original request.

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Holders may, however, sue to enforce the payment of principal, premium or interest on any debt security on or after the due date or to enforce the right, if any, to convert any debt security (if the debt security is convertible) without following the procedures listed in (1) through (3) above.

We will furnish the trustee an annual statement from our officers as to whether or not we are in default in the performance of the conditions and covenants under the indenture and, if so, specifying all known defaults.

Modification and Waiver

Unless we indicate otherwise in a prospectus supplement, the applicable trustee and we may make modifications and amendments to an indenture with the consent of the holders of a majority in aggregate principal amount of the outstanding securities of each series affected by the modification or amendment.

We may also make modifications and amendments to the indentures for the benefit of holders without their consent, for certain purposes including, but not limited to:

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However, neither the trustee nor we may make any modification or amendment without the consent of the holder of each outstanding security of that series affected by the modification or amendment if such modification or amendment would:

Satisfaction and Discharge; Defeasance

We may be discharged from our obligations on the debt securities, subject to limited exceptions, of any series that have matured or will mature or be redeemed within one year if we deposit enough money with the trustee to pay all the principal, interest and any premium due to the stated maturity date or redemption date of the debt securities.

Each indenture contains a provision that permits us to elect either or both of the following:

To make either of the above elections, we must irrevocably deposit in trust with the trustee enough money to pay in full the principal, interest and premium on the debt securities. This amount may be made in cash and/or U.S. government obligations or, in the case of debt securities denominated in a currency other than U.S. dollars, cash in the currency in which such series of securities is denominated and/or foreign government obligations. As a condition to either of the above elections, for debt securities denominated in U.S. dollars we must deliver to the trustee an opinion of counsel that the holders of the debt securities will not recognize income, gain or loss for U.S. federal income tax purposes as a result of the action.

With respect to debt securities of any series that are denominated in a currency other than United States dollars, “foreign government obligations” means:

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Notices

Notices to holders will be given by mail to the addresses of the holders in the security register.

Governing Law

The indentures and the debt securities will be governed by, and construed under, the laws of the State of New York.

No Personal Liability of Directors, Officers, Employees and Stockholders

No incorporator, stockholder, employee, agent, officer, director or subsidiary of ours will have any liability for any obligations of ours, or because of the creation of any indebtedness under the debt securities, the indentures or supplemental indentures. The indentures provide that all such liability is expressly waived and released as a condition of, and as a consideration for, the execution of such indentures and the issuance of the debt securities.

Regarding the Trustee

The indentures limit the right of the trustee, should it become our creditor, to obtain payment of claims or secure its claims.

The trustee will be permitted to engage in certain other transactions with us. However, if the trustee acquires any conflicting interest, and there is a default under the debt securities of any series for which it is trustee, the trustee must eliminate the conflict or resign.

Subordinated Debt Securities

The following provisions will be applicable with respect to each series of subordinated debt securities, unless otherwise stated in the prospectus supplement relating to that series of subordinated debt securities.

The indebtedness evidenced by the subordinated debt securities of any series is subordinated, to the extent provided in the subordinated indenture and the applicable prospectus supplement, to the prior payment in full, in cash or other payment satisfactory to the holders of senior debt, of all senior debt, including any senior debt securities.

Upon any distribution of our assets upon any dissolution, winding up, liquidation or reorganization, whether voluntary or involuntary, marshalling of assets, assignment for the benefit of creditors, or in bankruptcy, insolvency, receivership or other similar proceedings, payments on the subordinated debt securities will be subordinated in right of payment to the prior payment in full in cash or other payment satisfactory to holders of senior debt of all senior debt.

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In the event of any acceleration of the subordinated debt securities of any series because of an event of default with respect to the subordinated debt securities of that series, holders of any senior debt would be entitled to payment in full in cash or other payment satisfactory to holders of senior debt of all senior debt before the holders of subordinated debt securities are entitled to receive any payment or distribution.

In addition, the subordinated debt securities will be structurally subordinated to all indebtedness and other liabilities of our subsidiaries, including trade payables and lease obligations. This occurs because our right to receive any assets of our subsidiaries upon their liquidation or reorganization, and your right to participate in those assets, will be effectively subordinated to the claims of that subsidiary’s creditors, including trade creditors, except to the extent that we are recognized as a creditor of such subsidiary. If we are recognized as a creditor of that subsidiary, our claims would still be subordinate to any security interest in the assets of the subsidiary and any indebtedness of the subsidiary senior to us.

We are required to promptly notify holders of senior debt or their representatives under the subordinated indenture if payment of the subordinated debt securities is accelerated because of an event of default.

Under the subordinated indenture, we may not make payment on the subordinated debt securities if:

We will resume payments on the subordinated debt securities:

No new payment blockage period may commence on the basis of a non-payment default unless 365 days have elapsed from the effectiveness of the immediately prior payment blockage notice. No non-payment default that existed or was continuing on the date of delivery of any payment blockage notice to the trustee shall be the basis for a subsequent payment blockage notice.

As a result of these subordination provisions, in the event of our bankruptcy, dissolution or reorganization, holders of senior debt may receive more, ratably, and holders of the subordinated debt securities may receive less, ratably, than our other creditors. The subordination provisions will not prevent the occurrence of any event of default under the subordinated indenture.

The subordination provisions will not apply to payments from money or government obligations held in trust by the trustee for the payment of principal, interest and premium, if any, on subordinated debt securities pursuant to the provisions described under the section entitled “Satisfaction and Discharge; Defeasance,” if the subordination provisions were not violated at the time the money or government obligations were deposited into trust.

If the trustee or any holder receives any payment that should not have been made to them in contravention of subordination provisions before all senior debt is paid in full in cash or other payment satisfactory to holders of senior debt, then such payment will be held in trust for the holders of senior debt.

Senior debt securities will constitute senior debt under the subordinated indenture.

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Additional or different subordination provisions may be described in a prospectus supplement relating to a particular series of debt securities.

Definitions

“Designated senior debt” means our obligations under any particular senior debt in which the instrument creating or evidencing the same or the assumption or guarantee thereof, or related agreements or documents to which we are a party, expressly provides that such indebtedness shall be designated senior debt for purposes of the subordinated indenture. The instrument, agreement or other document evidencing any designated senior debt may place limitations and conditions on the right of such senior debt to exercise the rights of designated senior debt.

“Indebtedness” means the following, whether absolute or contingent, secured or unsecured, due or to become due, outstanding on the date of the indenture for such series of securities or thereafter created, incurred or assumed:

“Senior debt” means the principal of, premium, if any, and interest, including all interest accruing subsequent to the commencement of any bankruptcy or similar proceeding, whether or not a claim for post-petition interest is allowable as a claim in any such proceeding, and rent payable on or in connection with, and all fees and other amounts payable in connection with, our indebtedness. However, senior debt shall not include:

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“Subsidiary” means a corporation more than 50% of the outstanding voting stock of which is owned, directly or indirectly, by us or by one or more of our other subsidiaries or by a combination of us and our other subsidiaries. For purposes of this definition, “voting stock” means stock or other similar interests which ordinarily has or have voting power for the election of directors, or persons performing similar functions, whether at all times or only so long as no senior class of stock or other interests has or have such voting power by reason of any contingency.

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DESCRIPTION OF THE WARRANTS

General

We may issue warrants for the purchase of our debt securities, preferred stock or common stock, or any combination thereof. Warrants may be issued independently or together with our debt securities, preferred stock or common stock and may be attached to or separate from any offered securities. Each series of warrants will be issued under a separate warrant agreement to be entered into between us and a bank or trust company, as warrant agent. The warrant agent will act solely as our agent in connection with the warrants. The warrant agent will not have any obligation or relationship of agency or trust for or with any holders or beneficial owners of warrants. This summary of certain provisions of the warrants is not complete. For the terms of a particular series of warrants, you should refer to the prospectus supplement for that series of warrants and the warrant agreement for that particular series.

Debt Warrants

The prospectus supplement relating to a particular issue of warrants to purchase debt securities will describe the terms of the debt warrants, including the following:

Debt warrant certificates will be exchangeable for new debt warrant certificates of different denominations. Debt warrants may be exercised at the corporate trust office of the warrant agent or any other office indicated in the prospectus supplement. Prior to the exercise of their debt warrants, holders of debt warrants will not have any of the rights of holders of the debt securities purchasable upon exercise and will not be entitled to payment of principal or any premium, if any, or interest on the debt securities purchasable upon exercise.

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Equity Warrants

The prospectus supplement relating to a particular series of warrants to purchase our common stock or preferred stock will describe the terms of the warrants, including the following:

Holders of equity warrants will not be entitled:

The descriptions of the warrants in this prospectus and in any prospectus supplement are summaries of the material provisions of the applicable warrants. These descriptions do not restate those warrants in their entirety and may not contain all the information that you may find useful. We urge you to read the applicable warrants because they, and not the summaries, define your rights as holders of the warrants. For more information, please review the forms of the relevant warrants, which will be filed with the SEC promptly after the offering of warrants and will be available as described in the section titled “Where You Can Find More Information.”

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DESCRIPTION OF THE SUBSCRIPTION RIGHTS

We may issue subscription rights to purchase our common stock, preferred stock or debt securities. These subscription rights may be offered independently or together with any other security offered hereby and may or may not be transferable by the stockholder receiving the subscription rights in such offering. In connection with any offering of subscription rights, we may enter into a standby arrangement with one or more underwriters or other purchasers pursuant to which the underwriters or other purchasers may be required to purchase any securities remaining unsubscribed for after such offering.

The prospectus supplement relating to any subscription rights we offer, if any, will, to the extent applicable, include specific terms relating to the offering, including some or all of the following:

The descriptions of the subscription rights in this prospectus and in any prospectus supplement are summaries of the material provisions of the applicable subscription right agreements. These descriptions do not restate those subscription right agreements in their entirety and may not contain all the information that you may find useful. We urge you to read the applicable subscription right agreements because they, and not the summaries, define your rights as holders of the subscription rights. For more information, please review the forms of the relevant subscription right agreements, which will be filed with the SEC promptly after the offering of subscription rights and will be available as described in the section titled “Where You Can Find More Information.”

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DESCRIPTION OF UNITS

We may issue units comprised of one or more of the other classes of securities described in this prospectus in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each included security. The units may be issued under unit agreements to be entered into between us and a unit agent, as detailed in the prospectus supplement relating to the units being offered. The prospectus supplement will describe:

The descriptions of the units in this prospectus and in any prospectus supplement are summaries of the material provisions of the applicable unit agreements. These descriptions do not restate those unit agreements in their entirety and may not contain all the information that you may find useful. We urge you to read the applicable unit agreements because they, and not the summaries, define your rights as holders of the units. For more information, please review the forms of the relevant unit agreements, which will be filed with the SEC promptly after the offering of units and will be available as described in the section titled “Where You Can Find More Information.”

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SELLING STOCKHOLDERS

This prospectus also relates to the possible resale by certain of our stockholders, who we refer to in this prospectus as the “selling stockholders,” of up to 33,738,329 shares of our common stock that were issued and outstanding prior to the original date of filing of the registration statement of which this prospectus forms a part. When we refer to the “selling stockholders” in this prospectus, we mean the persons listed in the table below, as well as their donees, pledgees, assignees, transferees, distributees, or other successors in interest.

The following table details the name of each selling stockholder, the number of shares of our common stock beneficially owned by the selling stockholder, and the number of shares of our common stock that may be offered by the selling stockholder for resale under this prospectus. The following table has been prepared on the assumption that all shares offered for resale by the selling stockholders under this prospectus will be sold to parties unaffiliated with the selling stockholders. The percentage of shares of our common stock beneficially owned by the selling stockholders both prior to and following the offering of securities pursuant to this prospectus, is based on 52,860,792 shares of our common stock outstanding as of November 6, 2017 and does not take into account any securities issued by us pursuant to this prospectus. We cannot advise you as to whether the selling stockholders will in fact sell any or all of such shares of our common stock.

Shares of common stock subject to options currently exercisable or exercisable within 60 days of November 6, 2017 which are subject to vesting conditions expected to occur within 60 days of November 6, 2017 are deemed to be outstanding and beneficially owned by the person holding the options for the purpose of computing the percentage of beneficial ownership of that person and any group of which that person is a member, but are not deemed outstanding for the purpose of computing the percentage of beneficial ownership for any other person.

Unless otherwise indicated in the footnotes below, each stockholder named in the following table possesses sole voting and investment power over the shares listed. The information does not necessarily indicate beneficial ownership for any other purpose. Unless otherwise noted below, the address of each stockholder listed on the table is c/o BlackLine, Inc., 21300 Victory Boulevard, 12^th Floor, Woodland Hills, CA 91367.

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No selling stockholder has had any material relationship with us or any of our affiliates within the past three fiscal years, other than as described below. The following is a summary of transactions since January 1, 2014 to which we have been or will be a party, in which the amount involved exceeded or will exceed $120,000, and in which any of the selling stockholders, or any immediate family member of, or person sharing the household with, any of these individuals or entities, had or will have a direct or indirect material interest.

Stockholders’ Agreement

We are party to the Stockholders’ Agreement, which contains specific rights, obligations and agreements of our Principal Stockholders as owners of our common stock. In addition, the Stockholders’ Agreement contains provisions related to the composition of our board of directors and its committees.

Voting Agreement. Under the Stockholders’ Agreement, our Principal Stockholders have agreed to take all necessary action, including casting all votes to which such existing owners are entitled to cast at any annual or special meeting of stockholders, so as to ensure that the composition of our board of directors and its committees complies with (and includes all of the nominees in accordance with) the provisions of the Stockholders’ Agreement related to the composition of our board of directors and its committees.

Silver Lake Sumeru Approvals. Under the Stockholders’ Agreement and subject to our amended and restated certificate of incorporation and amended and restated bylaws, and applicable law, for so long as the Principal Stockholders collectively own or hold of record, directly or indirectly, in the aggregate at least 40% of their collective “Post-IPO Shares” (as defined in the Stockholders’ Agreement), as adjusted for any reorganization, recapitalization, stock dividend, stock split, reverse stock split or similar changes in the Company’s capitalization, the following actions will require the approval of our board of directors, including the affirmative vote of at least two Silver Lake Sumeru directors:

Transfer Restrictions. Under the Stockholders’ Agreement, each of Iconiq, Ms. Tucker and Mr. Spanicciati have agreed, subject to certain limited exceptions, not to transfer, sell, exchange, assign, pledge,

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hypothecate, convey or otherwise dispose of or encumber any shares of our common stock without the consent of Silver Lake Sumeru until the earlier of (i) two years following the completion our initial public offering, or November 2, 2018, and (ii) Silver Lake Sumeru’s reduction of its holdings of common stock following our initial public offering by 50%; provided, however, that Ms. Tucker and Mr. Spanicciati will each have the right to sell a number of shares equal to up to 1% of the total outstanding shares of our common stock annually pursuant to Rule 144 of the Securities Act, and Ms. Tucker, Mr. Spanicciati and Iconiq will each have the right to sell all of the shares of our common stock offered by each for resale under this prospectus.

Drag Along Right. For so long as Silver Lake Sumeru holds greater than 10% of our common stock then outstanding, if Silver Lake Sumeru approves a change of control transaction, each of Iconiq, Ms. Tucker and Mr. Spanicciati will be required to vote in favor of and not oppose such transaction and, if structured as a sale of shares, sell its shares to a prospective buyer on the same terms that are applicable to Silver Lake Sumeru.

Registration Rights Agreement

We are party to an Amended and Restated Registration Rights Agreement with our Principal Stockholders, dated as of October 27, 2016, or the Registration Rights Agreement. Under the Registration Rights Agreement our Principal Stockholders are entitled to rights with respect to the registration of their shares under the Securities Act. We are registering all of the shares of our common stock to be sold by the selling stockholders under this prospectus pursuant to the Registration Rights Agreement. We will pay the registration expenses (other than underwriting discounts and commissions and stock transfer taxes) of the holders of the shares registered pursuant to the registrations described below.

Silver Lake Sumeru will be entitled to certain S-1 and S-3 registration rights on one or more occasions. Beginning one year following the completion of our initial public offering, or November 2, 2017, Iconiq will be entitled to certain S-3 registration rights on one or more occasions. Beginning two years following the completion of our initial public offering, or November 2, 2018, Ms. Tucker and Mr. Spanicciati will also be entitled to certain S-3 registration rights on one or more occasions. In addition, if we or a Principal Stockholder proposes to register the offer and sale of our capital stock under the Securities Act, the other Principal Stockholders will be entitled to certain “piggyback” registration rights allowing the holders to include their shares in such registration, subject to certain marketing and other limitations set forth in the registration rights agreement.

The registration rights described above apply to (i) shares of our common stock held by our Principal Stockholders and their respective affiliates, and (ii) any of our capital stock (or that of our subsidiaries) issued or issuable with respect to the common stock described in clause (i) with respect to any dividend, distribution, recapitalization, reorganization, or certain other corporate transactions, or Registrable Securities. These registration rights are also for the benefit of any subsequent holder of Registrable Securities; provided that any particular securities will cease to be Registrable Securities when they have been sold in a registered public offering, sold in compliance with Rule 144 of the Securities Act or repurchased by us or our subsidiaries. In addition, with the consent of the company and holders of a majority of Registrable Securities, any Registrable Securities held by a person other than Silver Lake Sumeru and its affiliates will cease to be Registrable Securities if they can be sold without limitation under Rule 144 of the Securities Act.

Stock Subscription Agreement

On October 21, 2014, we entered into a stock subscription agreement with Iconiq pursuant to which we issued 357,142 shares of our common stock to Iconiq at $14.00 per share, for aggregate gross cash proceeds of $5,000,000.

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Legal Services Reimbursement

As of December 31, 2015, we accrued for costs of third party legal services incurred on behalf of Silver Lake Sumeru, Iconiq and Mr. Spanicciati relating to our initial public offering and other corporate related matters. Total amounts accrued at December 31, 2015 were $161,000, of which $84,000 were expensed during 2015 and $77,000 were included in other assets as deferred offering costs.

Employment Arrangement

Isaac Tucker, who is the son of Ms. Tucker, our Chief Executive Officer, has been employed by us since 2006 and currently serves as Vice President of Product Management. His 2014, 2015 and 2016 total compensation, which is comprised of a base salary, bonus, equity and commissions, as applicable, was $424,436, $282,920 and $243,408, respectively, and was in line with similar roles at the company. In October 2016, we granted to Mr. Tucker an option award covering 20,000 shares of our common stock at an exercise price of $14.00 per share.

Participation in our Initial Public Offering

Certain entities affiliated with Iconiq, a holder of more than 5% of our common stock and an affiliate of a member of our board of directors, purchased 825,000 shares of our common stock in our initial public offering at the initial public offering price. The underwriters received the same discount from the shares sold to such affiliates as they did from all other shares sold to the public in the offering.

Certain Relationships

Ms. Tucker is our Chief Executive Officer and a member of our board of directors.

Mr. Spanicciati is our Chief Marketing Officer and a member of our board of directors.

Mr. Griffith is a member of our board of directors and a general partner of Iconiq.

From time to time, we do business with other companies affiliated with Silver Lake Sumeru and Iconiq. We believe that all such arrangements have been entered into in the ordinary course of business and have been conducted on an arms-length basis.

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PLAN OF DISTRIBUTION

We or the selling stockholders may sell the securities offered through this prospectus and any accompanying prospectus supplement, if required, in any of the following ways: (1) to or through underwriters or dealers, (2) directly to purchasers, including our affiliates, (3) through agents, or (4) through a combination of any of these methods. The securities may be distributed at a fixed price or prices, which may be changed, market prices prevailing at the time of sale, prices related to the prevailing market prices, or negotiated prices.

We or the selling stockholders may use any one or more of the following methods when selling securities:

If required, a prospectus supplement with respect to a particular offering will set forth the terms of the offering, including the following:

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A selling stockholder that is an entity may elect to make a pro rata in-kind distribution of shares of our common stock to its members, partners or stockholders pursuant to the registration statement of which this prospectus forms a part by delivering a prospectus. To the extent that such members, partners or stockholders are not affiliates of such selling stockholder, such members, partners or stockholders would thereby receive freely tradeable shares of our common stock pursuant to the distribution through a registration statement.

Sale through Underwriters or Dealers

If underwriters are used in the sale, the underwriters will acquire the securities for their own account, including through underwriting, purchase, security lending or repurchase agreements with us or the selling stockholders. The underwriters may resell the securities from time to time in one or more transactions, including negotiated transactions. Underwriters may sell the securities in order to facilitate transactions in any of our other securities (described in this prospectus or otherwise), including other public or private transactions and short sales. Underwriters may offer securities to the public either through underwriting syndicates represented by one or more managing underwriters or directly by one or more firms acting as underwriters. Unless otherwise indicated in the prospectus supplement, the obligations of the underwriters to purchase the securities will be subject to certain conditions, and the underwriters will be obligated to purchase all the offered securities if they purchase any of them (other than any securities purchased upon exercise of any option to purchase additional securities). In connection with any offering of common stock pursuant to this prospectus, underwriters may have an option to purchase additional shares of common stock from us. We will provide information regarding any such option to purchase additional shares of common stock from us in the applicable prospectus supplement. The underwriters may change from time to time any initial public offering price and any discounts or concessions allowed or reallowed or paid to dealers. The prospectus supplement will include the names of the principal underwriters, the respective amount of securities underwritten, the nature of the obligation of the underwriters to take the securities and the nature of any material relationship between an underwriter and us or the selling stockholders, as applicable.

Some or all of the securities that we offer through this prospectus may be new issues of securities with no established trading market. Any underwriters to whom we sell securities for public offering and sale may make a market in those securities, but they will not be obligated to do so and they may discontinue any market making at any time without notice. Accordingly, we cannot assure you of the liquidity of, or continued trading markets for, any securities offered pursuant to this prospectus.

If dealers are used in the sale of securities offered through this prospectus, we or the selling stockholders will sell the securities to them as principals. They may then resell those securities to the public at varying prices determined by the dealers at the time of resale. The prospectus supplement will include the names of the dealers and the terms of the transaction.

To our knowledge, there are currently no plans, arrangements or understandings between the selling stockholders and any underwriter, dealer or agent regarding the sale of the shares covered by this prospectus by such selling stockholders. If any selling stockholder notifies us that a material arrangement has been entered into with an underwriter, dealer or other agent for the sale of shares through a block trade, special offering or secondary distribution, we may be required to file a prospectus supplement pursuant to applicable SEC rules promulgated under the Securities Act.

Direct Sales and Sales through Agents

We or the selling stockholders may sell the securities offered through this prospectus directly. In this case, no underwriters or agents would be involved. Such securities may also be sold through agents designated from

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time to time. Any required prospectus supplement will name any agent involved in the offer or sale of the offered securities and will describe any commissions payable to the agent by us or the selling stockholders. Unless otherwise indicated in the prospectus supplement, any agent will agree to use its reasonable best efforts to solicit purchases for the period of its appointment.

We or the selling stockholders may sell the securities directly to institutional investors or others who may be deemed to be underwriters within the meaning of the Securities Act with respect to any sale of those securities.

Delayed Delivery Contracts

If the prospectus supplement indicates, we or the selling stockholders may authorize agents, underwriters or dealers to solicit offers from certain types of institutions to purchase securities at the public offering price under delayed delivery contracts. These contracts would provide for payment and delivery on a specified date in the future. The contracts would be subject only to those conditions described in the prospectus supplement. The applicable prospectus supplement will describe the commission payable for solicitation of those contracts.

At-the-Market Offerings

We or the selling stockholders may engage in at-the-market offerings into an existing trading market in accordance with Rule 415(a)(4). To the extent that we or the selling stockholders make sales through one or more underwriters or agents in at-the-market offerings, we will do so pursuant to the terms of a sales agency financing agreement or other at-the-market offering arrangement between us or the selling stockholders, on one hand, and the underwriters or agents, on the other. If we engage in at-the-market sales pursuant to any such agreement, we or the selling stockholders will sell our securities through one or more underwriters or agents, which may act on an agency basis or a principal basis. During the term of any such agreement, we or the selling stockholders may sell securities on a daily basis in exchange transactions or otherwise as we agree with the underwriters or agents. Any such agreement will provide that any securities sold will be sold at prices related to the then prevailing market prices for our securities. Therefore, exact figures regarding proceeds that will be raised or commissions to be paid cannot be determined as of the date of this prospectus. Pursuant to the terms of the agreement, we or the selling stockholders may agree to sell, and the relevant underwriters or agents may agree to solicit offers to purchase, blocks of our common stock or other securities. The terms of any such agreement will be set forth in more detail in the applicable prospectus or prospectus supplement.

Market Making, Stabilization and Other Transactions

Unless the applicable prospectus supplement states otherwise, each series of offered securities by us will be a new issue and will have no established trading market. We may elect to list any series of offered securities on an exchange. Any underwriters that we use in the sale of offered securities may make a market in such securities, but may discontinue such market making at any time without notice. Accordingly, we cannot assure you that the securities will have a liquid trading market.

Any underwriter may also over-allot or engage in stabilizing transactions, syndicate covering transactions and penalty bids in accordance with Rule 104 under the Exchange Act. Over-allotment or short sales involve sales by persons participating in the offering of more securities than were sold to them. In these circumstances, these persons would cover such over-allotments or short positions by making purchases in the open market or by exercising their over-allotment option, if any. Stabilizing transactions involve bids to purchase the underlying security in the open market for the purpose of pegging, fixing or maintaining the price of the securities. Syndicate covering transactions involve purchases of the securities in the open market after the distribution has been completed in order to cover syndicate short positions.

Penalty bids permit the underwriters to reclaim a selling concession from a syndicate member when the securities originally sold by the syndicate member are purchased in a syndicate covering transaction to cover

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syndicate short positions. Stabilizing transactions, syndicate covering transactions and penalty bids may cause the price of the securities to be higher than it would be in the absence of the transactions. The underwriters may, if they commence these transactions, discontinue them at any time.

Derivative Transactions and Hedging

We, the selling stockholders, the underwriters or other agents may engage in derivative transactions involving the securities. These derivatives may consist of short sale transactions and other hedging activities. The underwriters or agents may acquire a long or short position in the securities, hold or resell securities acquired and purchase options or futures on the securities and other derivative instruments with returns linked to or related to changes in the price of the securities. In order to facilitate these derivative transactions, we or the selling stockholders may enter into security lending or repurchase agreements with the underwriters or agents. The underwriters or agents may effect the derivative transactions through sales of the securities to the public, including short sales, or by lending the securities in order to facilitate short sale transactions by others. The underwriters or agents may also use the securities purchased or borrowed from us or others (or, in the case of derivatives, securities received from us in settlement of those derivatives) to directly or indirectly settle sales of the securities or close out any related open borrowings of the securities.

In addition, the selling stockholders may enter into hedging transactions with dealers which may engage in short sales of shares of our common stock in the course of hedging the positions they assume with the selling stockholders. The selling stockholders may also sell shares of our common stock short and deliver shares of our common stock to close out such short position. The selling stockholders may also enter into option or other transactions with dealers that require the delivery by such dealers of shares of our common stock, which securities may be resold thereafter pursuant to this prospectus or any applicable prospectus supplement.

Electronic Auctions

We or the selling stockholders may also make sales through the Internet or through other electronic means. Since we or the selling stockholders may from time to time elect to offer securities directly to the public, with or without the involvement of agents, underwriters or dealers, utilizing the Internet or other forms of electronic bidding or ordering systems for the pricing and allocation of such securities, you should pay particular attention to the description of that system we will provide in a prospectus supplement.

Such electronic system may allow bidders to directly participate, through electronic access to an auction site, by submitting conditional offers to buy that are subject to acceptance by us or the selling stockholders, and which may directly affect the price or other terms and conditions at which such securities are sold. These bidding or ordering systems may present to each bidder, on a so-called “real-time” basis, relevant information to assist in making a bid, such as the clearing spread at which the offering would be sold, based on the bids submitted, and whether a bidder’s individual bids would be accepted, prorated or rejected. For example, in the case of a debt security, the clearing spread could be indicated as a number of “basis points” above an index treasury note. Of course, many pricing methods can and may also be used.

Upon completion of such an electronic auction process, securities will be allocated based on prices bid, terms of bid or other factors. The final offering price at which securities would be sold and the allocation of securities among bidders would be based in whole or in part on the results of the Internet or other electronic bidding process or auction.

General Information

Agents, underwriters and dealers may be entitled, under agreements entered into with us or the selling stockholders, to indemnification by us or the selling stockholders against certain liabilities, including liabilities under the Securities Act. Agents, underwriters and dealers, or their affiliates, may engage in transactions with or

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perform services for us in the ordinary course of their businesses. In no event will the total amount of compensation paid to the agents, underwriters and dealers upon completion of any offering exceed 8.0% of the gross proceeds of such offering.

The selling stockholders and any agents, underwriters or dealers that are involved in selling shares of our common stock may be deemed to be “underwriters” within the meaning of the Securities Act in connection with such sales. In such event, any commissions received by such agents, underwriters or dealers and any profit on the resale of shares of our common stock purchased by them may be deemed to be underwriting commissions or discounts under the Securities Act.

There can be no assurance that any selling stockholder will sell any or all of the shares of our common stock registered pursuant to the registration statement of which this prospectus forms a part. The selling stockholders may also sell shares under Rule 144 under the Securities Act, if available, rather than pursuant to the registration statement of which this prospectus forms a part. If sold under the registration statement of which this prospectus forms a part, the securities will be freely tradable in the hands of persons other than our affiliates.

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LEGAL MATTERS

The validity of the securities offered hereby will be passed upon by Wilson Sonsini Goodrich & Rosati, P.C., Palo Alto, California. Wilson Sonsini Goodrich & Rosati, P.C. and certain of its members are associated with WS Investment Company, LLC (2007A), which is an investor in certain investment funds affiliated with Silver Lake Sumeru and directly or indirectly owns less than 0.1% of the outstanding shares of our common stock. Additional legal matters may be passed on for any underwriters, dealers or agents by counsel we will name in any applicable prospectus supplement.

EXPERTS

The financial statements incorporated in this prospectus by reference to the Annual Report on Form 10-K for the year ended December 31, 2016 have been so incorporated in reliance on the report of PricewaterhouseCoopers LLP, an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

WHERE YOU CAN FIND MORE INFORMATION

We have filed with the SEC a registration statement on Form S-3 under the Securities Act with respect to the securities described in this prospectus. This prospectus, which constitutes a part of the registration statement, does not contain all of the information set forth in the registration statement, some of which is contained in exhibits to the registration statement as permitted by the rules and regulations of the SEC. For further information with respect to us and our securities, we refer you to the registration statement, including the exhibits filed as a part of the registration statement. Statements contained in this prospectus concerning the contents of any contract or any other document are not necessarily complete. If a contract or document has been filed as an exhibit to the registration statement, please see the copy of the contract or document that has been filed. A copy of the registration statement and the exhibits filed therewith may be inspected without charge at the public reference room maintained by the SEC, located at 100 F Street, N.E., Room 1580, Washington, D.C. 20549, and copies of all or any part of the registration statement may be obtained from that office at prescribed rates. You may obtain information on the operation of the SEC’s public reference room by calling the SEC at 1-800-SEC-0330. The SEC also maintains an Internet website that contains reports, proxy statements and other information about issuers that file electronically with the SEC. The address of that website is www.sec.gov.

We are subject to the information and periodic reporting requirements of the Exchange Act and, in accordance therewith, file periodic reports, proxy statements and other information with the SEC. These periodic reports, proxy statements and other information will be available for inspection and copying at the SEC’s public reference room and accessible through the SEC’s Internet website referenced above. We also maintain an Internet website at www.blackline.com, at which you may access these materials free of charge as soon as reasonably practicable after they are electronically filed with, or furnished to, the SEC. Information contained on, or that can be accessed through, our website does not constitute a part of this prospectus or the registration statement of which this prospectus forms a part, and is not incorporated by reference herein. We have included our website address in this prospectus solely for informational purposes and you should not consider any information contained on, or that can be accessed through, our website as part of this prospectus or in deciding whether to purchase our securities.

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INFORMATION INCORPORATED BY REFERENCE

We “incorporate by reference” certain documents we file with the SEC, which means that we are disclosing important information to you by referring you to those documents. The information incorporated by reference is an important part of this prospectus, and any information contained in this prospectus or in any document incorporated by reference in this prospectus will be deemed to be modified or superseded to the extent that a statement contained in this prospectus or free writing prospectus provided to you in connection with this offering, or in any other document we subsequently file with the SEC that also is incorporated by reference in this prospectus, modifies or supersedes the original statement. Any statement so modified or superseded will not be deemed, except as so modified or superseded, to be a part of this prospectus.

The following documents filed with the SEC are hereby incorporated by reference in this prospectus:

All reports and other documents subsequently filed by us pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act after the date of this prospectus and prior to the termination of this offering shall be deemed to be incorporated by reference in this prospectus and to be part hereof from the date of filing of such reports and other documents.

Notwithstanding the statements in the preceding paragraphs, no document, report or exhibit (or portion of any of the foregoing) or any other information that we have “furnished” or may in the future “furnish” to the SEC pursuant to the Exchange Act shall be incorporated by reference into this prospectus.

We hereby undertake to provide without charge to each person, including any beneficial owner, to whom a copy of this prospectus is delivered, upon written or oral request of any such person, a copy of any and all of the information that has been or may be incorporated by reference in this prospectus, other than exhibits to such documents, unless such exhibits have been specifically incorporated by reference thereto. Requests for such copies should be directed to our Investor Relations department, at the following address: BlackLine, Inc., 21300 Victory Boulevard, 12th Floor, Woodland Hills, California 91367, Attention: Investor Relations, or you may call us at (818) 223-9008.

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