As filed with the Securities and Exchange Commission on February 7, 2018

Registration No. 333-          

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

LIMELIGHT NETWORKS, INC.

(Exact name of registrant as specified in its charter)

222 South Mill Avenue, 8th Floor

Tempe, Arizona 85281

(602)850-5000

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Robert A. Lento

President and Chief Executive Officer

Limelight Networks, Inc.

222 South Mill Avenue, 8th Floor

Tempe, Arizona 85281

(602)850-5000

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Rick Kline

Andrew Hill

Goodwin Procter LLP

135 Commonwealth Dr.

Menlo Park, CA 94025

Approximate date of commencement of proposed sale to the public: From time to time on or after the effective date of this registration statement.

If the only securities being registered on this form are being offered pursuant to dividend or interest reinvestment plans, please check the following box:  ☐

If any of the securities being registered on this form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box:  ☒

If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering:  ☐

If this form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering:  ☐

If this form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Securities and Exchange Commission pursuant to Rule 462(e) under the Securities Act, check the following box:  ☐

If this form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box:  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2 of the Exchange Act. (Check one):

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

CALCULATION OF REGISTRATION FEE

The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

The information in this preliminary prospectus is not complete and may be changed. The selling stockholder may not sell these securities until the registration statement filed with the Securities and Exchange Commission is declared effective. This preliminary prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

Subject to Completion, Dated February 7, 2018

Limelight Networks, Inc.

15,917,469 Shares

Common Stock

The selling stockholder identified in this prospectus may offer and sell, from time to time, in one or more offerings, up to 15,917,469 shares of our common stock. You should carefully read this prospectus and any accompanying prospectus supplement before you decide to invest in any of these securities.

The distribution of the common stock by the selling stockholder may be effected from time to time by a variety of methods, including, without limitation:

The selling stockholder will bear all commissions and discounts, if any, attributable to the sales of shares as well as all other costs, expenses and fees in connection with the registration of the shares. The brokers or dealers through or to whom the shares of common stock may be sold may be deemed underwriters of the shares within the meaning of the Securities Act of 1933, as amended, in which event all brokerage commissions or discounts and other compensation received by those brokers or dealers may be deemed to be underwriting compensation. To the extent required, the names of any underwriters and applicable commissions or discounts and any other required information with respect to any particular sale will be set forth in an accompanying prospectus supplement. See “Plan of Distribution” for a further description of how the selling stockholder may dispose of the shares covered by this prospectus.

We are not selling any common stock under this prospectus and will not receive any of the proceeds from the sale of the common stock by the selling stockholder.

Our common stock is listed on the NASDAQ Global Select Market under the symbol “LLNW.” On February 6, 2018, the last reported sales price of a share of our common stock on the NASDAQ Global Select Market was $4.46.

Investing in our common stock involves risk. See “Risk Factors” beginning on page 7.

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

The date of this prospectus is                 , 2018.

TABLE OF CONTENTS

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or the SEC, using a “shelf” registration process. Under this shelf registration process, the selling stockholder may sell certain shares of our common stock in one or more offerings. When the selling stockholder sells shares of common stock under this shelf registration process, we may provide a prospectus supplement that will contain more specific information about the terms of such offering. The prospectus supplement may also add to, update or change any of the information contained in this prospectus. You should carefully read this prospectus and any accompanying prospectus supplement, as well as the information incorporated in this prospectus or the accompanying prospectus supplement by reference. See “Incorporation of Certain Information by Reference.” Any information in any accompanying prospectus supplement or any subsequent material incorporated herein by reference will supersede the information in this prospectus or any earlier prospectus supplement.

As used in this prospectus and any accompanying prospectus supplement, unless the context otherwise indicates, references to “our,” “we,” “us,” the “Company” and “our business” mean Limelight Networks, Inc. (“Limelight”).

Limelight has not authorized anyone to provide any information other than that contained or incorporated by reference in this prospectus, any prospectus supplement or any free writing prospectus prepared by or on behalf of Limelight or to which Limelight has referred you. Limelight takes no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. 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 issuer free writing prospectus in connection with the offering described herein and therein. Neither this prospectus nor any prospectus supplement nor any related issuer 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 issuer free writing prospectus, as well as the documents incorporated by reference, before making an investment decision. Neither the delivery of this prospectus or any prospectus supplement or any issuer 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 issuer free writing prospectus is correct as of any date subsequent to the date hereof or of such prospectus supplement or issuer 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. Limelight’s business, financial condition, results of operations and prospects may have changed since that date.

1

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and any accompanying prospectus supplement and the documents incorporated by reference contain statements reflecting assumptions, expectations, projections, intentions or beliefs about future events that are intended as “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. All statements included or incorporated by reference in this prospectus and the accompanying prospectus supplement, other than statements of historical fact, that address activities, events or developments that we expect, believe or anticipate will or may occur in the future are forward-looking statements. These statements represent our reasonable judgment on the future based on various factors and using numerous assumptions and are subject to known and unknown risks, uncertainties and other factors that could cause our actual results and financial position to differ materially from those contemplated by the statements. You can identify these statements by the fact that they do not relate strictly to historical or current facts. They use words such as “anticipate,” “believe,” “estimate,” “expect,” “intend,” “could,” “continue,” “forecast,” “may,” “should,” “plan,” “project” and other words of similar meaning. In particular, these include, but are not limited to, statements relating to the following:

These forward-looking statements are based on management’s current expectations, estimates, forecasts and projections about our business and the industry in which we operate and management’s beliefs and assumptions and are not guarantees of future performance or development and involve known and unknown risks,

2

uncertainties and other factors that are in some cases beyond our control. As a result, any or all of our forward looking statements in this prospectus and in the documents that are incorporated by reference herein may turn out to be inaccurate. Factors that may cause actual results to differ materially from current expectations include, among other things, those listed under “Risk Factors” and elsewhere in this prospectus, any accompanying prospectus supplement and in the documents that are incorporated by reference herein. Potential investors are urged to consider these factors carefully in evaluating the forward-looking statements. These forward-looking statements speak only as of the date of this prospectus. Except as required by law, we assume no obligation to update or revise these forward-looking statements for any reason, even if new information becomes available in the future. You should, however, review the factors and risks we describe in the reports we will file from time to time with the Securities and Exchange Commission, or SEC, after the date of this prospectus. See “Where You Can Find More Information” and “Incorporation of Certain Information by Reference.”

This prospectus, any accompanying prospectus supplement and the documents incorporated by reference herein also contain estimates, projections and other information concerning our industry, our business and the markets for certain diseases, including data regarding the estimated size of those markets, and the incidence and prevalence of certain medical conditions. Information that is based on estimates, forecasts, projections, market research, or similar methodologies is inherently subject to uncertainties and actual events or circumstances may differ materially from events and circumstances reflected in this information. Unless otherwise expressly stated, we obtained this industry, business, market and other data from reports, research surveys, studies and similar data prepared by market research firms and other third parties, industry, medical and general publications, government data and similar sources.

3

WHERE YOU CAN FIND MORE INFORMATION

This prospectus is part of a registration statement we have filed with the SEC under the Securities Act. The registration statement, including the attached exhibits, contains additional relevant information about us and the securities described in this prospectus. The SEC’s rules and regulations allow us to omit certain information included in the registration statement from this prospectus. The registration statement may be inspected by anyone without charge at the SEC’s principal office at 100 F Street, N.E., Washington, D.C. 20549.

In addition, we file annual, quarterly and current reports, proxy statements and other information with the SEC under the Exchange Act. You may read and copy this information at the following SEC location:

Public Reference Room

100 F Street, N.E.

Washington, D.C. 20549

You may also obtain copies of this information by mail from the SEC’s Public Reference Room at rates determined by the SEC. You may obtain information on the operation of the Public Reference Room by calling the SEC at 1-800-SEC-0330. You may also inspect reports, proxy statements and other information that we have filed electronically with the SEC at the SEC’s web site at http://www.sec.gov/.

INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

The SEC allows us to “incorporate by reference” into this prospectus the information we file with the SEC. This permits us to disclose important information to you by referencing these filed documents. Any information referenced in this way is considered part of this prospectus. Any subsequent information filed with the SEC will automatically be deemed to update and supersede the information in this prospectus and in our other filings with the SEC. We incorporate by reference the documents listed below and any filings made by us with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act from the initial filing of the registration statement of which this prospectus forms a part until all of the securities offered in this prospectus are sold; provided, however, we are not incorporating by reference any information furnished (but not filed) under Item 2.02 or Item 7.01 of any Current Report on Form 8-K:

Any statement contained in this prospectus, or in a document all or a portion of which is incorporated by reference in this prospectus, will be deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in a document incorporated by reference in this prospectus modifies or supersedes the statement. Any such statement or document so modified or superseded will not be deemed, except as so modified or superseded, to constitute a part of this prospectus.

4

You can request a copy of any document incorporated by reference in this prospectus, at no cost, by writing or telephoning us at the following:

Limelight Networks, Inc.

Attn: Investor Relations

222 South Mill Avenue, 8^th Floor

Tempe, Arizona 85281

(602) 850-5000

5

COMPANY OVERVIEW

Our Company

Limelight operates a private, globally distributed, high-performance network and provides a suite of integrated services marketed as the Limelight Orchestrate Platform. These services include content delivery, video content management, website and web application acceleration, website and content security, and cloud storage services.

The services we provide help our customers optimize and deliver digital content to a wide variety of digital devices. These services provide advanced features to enable digital workflows for video publishing, content distribution for any device, and website and web application acceleration. Limelight services incorporate content and application security, file management, video transformation, distributed storage functionality, and the analytics and reporting associated with them. These services leverage our global network, which provides highly available, highly redundant storage, bandwidth, and computing resources, as well as connectivity to last-mile broadband network providers. Limelight’s high capacity, high speed private global network and distributed storage and compute capabilities are also well suited to the emerging Internet of Things (IoT) and edge compute workloads where rapid response times are needed.

We derive revenue primarily from the sale of components of the Limelight Orchestrate Platform. We also generate revenue through the sale of professional services and other infrastructure services, such as transit and rack space services. In addition, we also maintain relationships with resellers that purchase our services for resale to their end customers.

We provide our services to customers that we believe view Internet, mobile, social, and other digital initiatives as critical to their success, including traditional and emerging media companies operating in the television, music, radio, newspaper, magazine, movie, game, software, and social media industries, as well as to enterprises, technology companies, and government entities conducting business online. Our offerings enable our customers to deliver a high quality online experience and thereby improve brand perception, drive revenue, and enhance customer relationships.

Additional Information

Limelight is a Delaware corporation formed in 2001. Our principal executive offices are located at 222 South Mill Avenue, 8^th Floor, Tempe, Arizona 85281, and our main telephone number is (602) 850-5000. We began development of our infrastructure in 2001 and began generating meaningful revenue in 2002. We began international operations in 2004. We are registered as a reporting company under the Exchange Act. Accordingly, we file or furnish with the SEC annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and all amendments to such reports as required by the Exchange Act and the rules and regulations of the SEC. We refer to these reports as “Periodic Reports”. The public may read and copy any Periodic Reports or other materials we file with the SEC at the SEC’s Public Reference Room at 100 F. Street, NE, Washington, DC 20549. Information on the operation of the Public Reference Room is available by calling 1-800-SEC-0330. In addition, the SEC maintains an Internet website that contains reports, proxy and information statements and other information regarding issuers, such as Limelight Networks, Inc., that file electronically with the SEC. The address of this website is www.sec.gov.

Our Internet website address is www.limelight.com. We make available, free of charge, on or through our Internet website our Periodic Reports and amendments to those Periodic Reports as soon as reasonably practicable after we electronically file them with the SEC. Our website and the information contained therein or connected thereto shall not be deemed to be incorporated into this prospectus or the accompanying prospectus supplement or the registration statement of which this prospectus forms a part, and you should not rely on any such information in making your decision whether to purchase our securities.

6

RISK FACTORS

Investing in our common stock involves a high degree of risk. You should carefully consider the risks, uncertainties and other factors described in our most recent Annual Report on Form 10-K, as supplemented and updated by subsequent Quarterly Reports on Form 10-Q and Current Reports on Form 8-K that we have filed or will file with the SEC, and in other documents which are incorporated by reference into this prospectus, as well as the risk factors and other information contained in or incorporated by reference into any accompanying prospectus supplement and any related free writing prospectus.

If any of these risks were to occur, our business, affairs, prospects, assets, financial condition, results of operations and cash flows could be materially and adversely affected. If this occurs, the trading price of our securities could decline, and you could lose all or part of your investment. For more information about our SEC filings, please see “Where You Can Find More Information.”

7

USE OF PROCEEDS

The selling stockholder will receive all net proceeds from the sale of the shares of common stock offered by this prospectus and any accompanying prospectus supplement. We will not receive any of the proceeds from the sale of our common stock by the selling stockholder.

8

DESCRIPTION OF CAPITAL STOCK

The following information describes our common stock and preferred stock, as well as certain provisions of our amended and restated certificate of incorporation, referred to as our certificate of incorporation, and amended and restated bylaws, referred to as our bylaws. This description is only a summary. You should also refer to our certificate of incorporation and bylaws, which have been filed with the SEC as exhibits to our registration statement, of which this prospectus forms a part.

General

Our authorized capital stock consists of 300,000,000 shares of common stock with a $0.001 par value per share, and 7,500,000 shares of undesignated preferred stock with a $0.001 par value per share. Our board of directors may establish the rights and preferences of the preferred stock from time to time. As of February 1, 2018 there were 110,826,546 shares of common stock issued and outstanding, held of record by 250 stockholders, although we believe that there may be a significantly larger number of beneficial owners of our common stock. We derived the number of stockholders by reviewing the listing of outstanding common stock recorded by our transfer agent as of February 1, 2018.

The following is a summary of the material provisions of the common stock and preferred stock provided for in our certificate of incorporation and bylaws. For additional detail about our capital stock, please refer to our certificate of incorporation and bylaws.

Common Stock

The holders of common stock are entitled to one vote per share on all matters to be voted upon by the stockholders. Subject to preferences that may be applicable to any outstanding preferred stock, the holders of common stock are entitled to receive ratably any dividends that may be declared from time to time by the board of directors out of funds legally available for that purpose. In the event of our liquidation, dissolution or winding up, the holders of common stock are entitled to share ratably in all assets remaining after payment of liabilities, subject to prior distribution rights of preferred stock then outstanding. The common stock has no preemptive or conversion rights or other subscription rights. There are no redemption or sinking fund provisions applicable to the common stock. All outstanding shares of common stock are fully paid and nonassessable.

Our common stock is listed on the Nasdaq Global Market under the symbol “LLNW.” The transfer agent and registrar for the common stock is American Stock Transfer and Trust Company. Its address is 6201 15th Avenue, Brooklyn, New York, New York 11219, and its telephone number is (800) 937-5449.

Preferred stock

The following description of preferred stock and the description of the terms of any particular series of preferred stock that we choose to issue hereunder and that will be set forth in the related prospectus supplement are not complete. These descriptions are qualified in their entirety by reference to our certificate of incorporation and the certificate of designation relating to any series of preferred stock. The rights, preferences, privileges and restrictions of the preferred stock of each series will be fixed by the certificate of designation relating to that series. The prospectus supplement also will contain a description of certain United States federal income tax consequences relating to the purchase and ownership of the series of preferred stock that is described in the prospectus supplement.

Under the terms of our certificate of incorporation, our board of directors is authorized to issue shares of preferred stock in one or more series without stockholder approval. Our board of directors has the discretion to determine the rights, preferences, privileges and restrictions, including voting rights, dividend rights, conversion rights, redemption privileges and liquidation preferences, of each series of preferred stock. There are no restrictions presently on the repurchase or redemption of any shares of our preferred stock.

9

The prospectus supplement for a series of preferred stock will specify:

The issuance of preferred stock will affect, and may adversely affect, the rights of holders of common stock. It is not possible to state the actual effect of the issuance of any shares of preferred stock on the rights of holders of common stock until our board of directors determines the specific rights attached to that preferred stock. The effects of issuing preferred stock could include one or more of the following:

We have no present plans to issue any shares of preferred stock nor are any shares of our preferred stock presently outstanding. Preferred stock will be fully paid and nonassessable upon issuance.

Effect of Certain Provisions of our Certificate of Incorporation and Bylaws and the Delaware Anti-Takeover Statute

Some provisions of Delaware law and our certificate of incorporation and bylaws contain provisions that could make the following transactions more difficult:

Those provisions, summarized below, could have the effect of delaying, deferring or discouraging another party from acquiring control of us. These provisions and certain provisions of Delaware law, which are summarized below, are expected to discourage coercive takeover practices and inadequate takeover bids and to promote stability in our management. These provisions are also designed, in part, to encourage persons seeking to acquire control of us to negotiate first with our board of directors.

10

Certificate of Incorporation and Bylaws

Our certificate of incorporation and our bylaws provide for the following:

Delaware Anti-Takeover Statute

We are subject to Section 203 of the General Corporation Law of the State of Delaware, which prohibits a Delaware corporation from engaging in any business combination with any interested stockholder for a period of three years after the date that such stockholder became an interested stockholder, with the following exceptions:

11

In general, Section 203 defines business combination to include the following:

In general, Section 203 defines interested stockholder as an entity or person who, together with affiliates and associates, beneficially owns, or within three years prior to the determination of interested stockholder status did own, 15% or more of the outstanding voting stock of the corporation.

Listing

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

12

SELLING STOCKHOLDER

The selling stockholder may sell some, all or none of its shares. We do not know how long the selling stockholder will hold the shares offered hereunder before selling them. The shares offered by this prospectus may be offered from time to time by the selling stockholder. As used in this prospectus, the term “selling stockholder” includes the selling stockholder listed below, and any donee, pledgee, transferee or other successor in interest selling shares received after the date of this prospectus from the selling stockholder as a gift, pledge, or other non-sale related transfer. The selling stockholder may have sold or transferred, in transactions exempt from the registration requirements of the Securities Act, some or all of its shares since the date on which the information in the table is presented. Information about the selling stockholder may change over time.

The following table sets forth the name of the selling stockholder, the number of shares of our common stock and the percentage of our common stock beneficially owned by the selling stockholder prior to this offering, the number of shares that may be offered under this prospectus by the selling stockholder, and the number of shares of our common stock and the percentage of our common stock to be beneficially owned by the selling stockholder after completion of this offering, assuming that all shares offered hereunder are sold as contemplated herein. The number of shares in the column “Maximum Number of Shares That May Be Offered” represents all of the shares that the selling stockholder may offer under this prospectus.

Beneficial ownership is determined under the rules of the SEC and generally includes voting or investment power over securities. Except in cases where community property laws apply or as indicated in the footnotes to this table, we believe that the stockholder identified in the table possesses sole voting and investment power over all shares of common stock shown as beneficially owned by the stockholder.

13

14

PLAN OF DISTRIBUTION

The selling stockholder may offer and sell, from time to time, some or all of the shares of common stock covered by this prospectus. Registration of the shares of common stock covered by this prospectus does not mean, however, that those shares necessarily will be offered or sold. We will not receive any proceeds from any sale by the selling stockholder of the securities. See “Use of Proceeds.” The selling stockholder will pay all costs, expenses and fees in connection with the registration of the shares of common stock, including fees of our counsel and accountants, fees payable to the SEC and fees of counsel to the selling stockholder. The selling stockholder will also pay all underwriting discounts and commissions and similar selling expenses, if any, attributable to the sale of the shares of common stock covered by this prospectus.

The selling stockholder may sell the shares of common stock covered by this prospectus from time to time, at market prices prevailing at the time of sale, at prices related to market prices, at a fixed price or prices subject to change or at negotiated prices, by a variety of methods including, without limitation, the following:

In effecting sales, brokers or dealers engaged by the selling stockholder may arrange for other brokers or dealers to participate. Broker-dealer transactions may include:

At any time a particular offer of the shares of common stock covered by this prospectus is made, a prospectus supplement, if required, will be distributed which will set forth the aggregate amount of shares of common stock covered by this prospectus being offered and the terms of the offering, including the name or names of any underwriters, dealers, brokers or agents, any option under which underwriters may purchase additional shares of common stock from the selling stockholder, any discounts, commissions, concessions and other items constituting compensation from the selling stockholder and any discounts, commissions or concessions allowed or reallowed or paid to dealers. Such prospectus supplement, and, if necessary, a post-effective amendment to the registration statement of which this prospectus is a part, will be filed with the SEC to reflect the disclosure of additional information with respect to the distribution of the shares of common stock covered by this prospectus.

In connection with the sale of the shares of common stock covered by this prospectus through underwriters, underwriters may receive compensation in the form of underwriting discounts or commissions and may also receive commissions from purchasers of shares of common stock for whom they may act as agent. Underwriters may sell to or through dealers, and such dealers may receive compensation in the form of discounts, concessions or commissions from the underwriters and/or commissions from the purchasers for whom they may act as agent.

Any underwriters, broker-dealers or agents participating in the distribution of the shares of common stock covered by this prospectus may be deemed to be “underwriters” within the meaning of the Securities Act, and

15

any commissions received by any of those underwriters, broker-dealers or agents may be deemed to be underwriting commissions under the Securities Act. The selling stockholder may also be deemed to be an underwriter, and any discounts and commissions it receives and any profit it realizes on the sale of the common stock may be deemed to be underwriting commissions under the Securities Act.

The selling stockholder may enter into derivative transactions with third parties, or sell shares of common stock to third parties in privately negotiated transactions. If the applicable prospectus supplement indicates, in connection with those derivatives, the third parties may sell shares of common stock covered by this prospectus and the applicable prospectus supplement, including in short sale transactions. If so, the third party may use shares of common stock pledged by the selling stockholder or borrowed from the selling stockholder or others to settle those sales or to close out any related open borrowings of stock, and may use shares of common stock received from the selling stockholder in settlement of those derivatives to close out any related open borrowings of stock. The third party in such sale transactions will be an underwriter and, if not identified in this prospectus, will be identified in the applicable prospectus supplement (or a post-effective amendment).

We may authorize underwriters, dealers and agents to solicit from third parties offers to purchase shares of common stock under contracts providing for payment and delivery on future dates. The applicable prospectus supplement will describe the material terms of these contracts, including any conditions to the purchasers’ obligations, and will include any required information about commissions we may pay for soliciting these contracts.

Underwriters, dealers, agents and other persons may be entitled, under agreements that they may enter into with us and the selling stockholder, to indemnification by us and the selling stockholder against certain liabilities, including liabilities under the Securities Act.

In connection with the offering, the underwriters may purchase and sell shares of common stock in the open market. These transactions may include short sales, stabilizing transactions and purchases to cover positions created by short sales. Short sales involve the sale by the underwriters of a greater number of shares than they are required to purchase in the offering. “Covered” short sales are sales made in an amount not greater than the underwriters’ option to purchase additional shares from the selling stockholder in the offering. The underwriters may close out any covered short position by either exercising their option to purchase additional shares or purchasing shares in the open market. In determining the source of shares to close out the covered short position, the underwriters will consider, among other things, the price of shares available for purchase in the open market as compared to the price at which they may purchase shares through the overallotment option. “Naked” short sales are any sales in excess of such option. The underwriters must close out any naked short position by purchasing shares in the open market. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of the common stock in the open market after pricing that could adversely affect investors who purchase in the offering. Stabilizing transactions consist of various bids for or purchases of common stock made by the underwriters in the open market prior to the completion of the offering.

The underwriters may also impose a penalty bid. This occurs when a particular underwriter repays to the underwriters a portion of the underwriting discount received by it because the representatives have repurchased shares sold by or for the account of such underwriter in stabilizing or short covering transactions.

Purchases to cover a short position and stabilizing transactions may have the effect of preventing or retarding a decline in the market price of the Company’s stock, and together with the imposition of the penalty bid, may stabilize, maintain or otherwise affect the market price of the common stock. As a result, the price of the common stock may be higher than the price that otherwise might exist in the open market. If these activities are commenced, they may be discontinued at any time. These transactions may be effected on NASDAQ, in the over-the-counter market or otherwise.

16

Certain underwriters, agents or dealers or their affiliates may have provided from time to time, and may provide in the future, investment, commercial banking, derivatives and financial advisory services to the Company, the selling stockholder and their respective affiliates in the ordinary course of business, for which they have received or may receive customary fees and commissions.

Some of the shares of common stock covered by this prospectus may be sold in private transactions or under Rule 144 under the Securities Act rather than pursuant to this prospectus.

LEGAL MATTERS

Certain legal matters with respect to the securities offered by this prospectus will be passed upon for us by Goodwin Procter LLP, Menlo Park, California.

EXPERTS

The consolidated financial statements of Limelight Networks, Inc. appearing in Limelight Networks, Inc.’s Annual Report (Form 10-K) for the year ended December 31, 2016 (including the schedule appearing therein) have been audited by Ernst & Young LLP, independent registered public accounting firm, as set forth in their report thereon, included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing.

17

PART II

INFORMATION NOT REQUIRED IN THE PROSPECTUS

The following table shows the costs and expenses, other than underwriting discounts and commissions, payable in connection with the sale and distribution of the securities being registered. Except as otherwise noted, we will pay all of these amounts. All amounts except the SEC registration fee and the FINRA fee are estimated.

Section 145(a) of the Delaware General Corporation Law (“DGCL”) provides, in general, that a corporation shall have the power to indemnify any person who was or is a party or is threatened to be made a party to any threatened, pending or completed action, suit or proceeding, whether civil, criminal, administrative or investigative (other than an action by or in the right of the corporation), because the person is or was a director, officer, employee or agent of the corporation or is or was serving at the request of the corporation as a director, officer, employee or agent of any other enterprise. Such indemnity may be against expenses (including attorneys’ fees), judgments, fines and amounts paid in settlement actually and reasonably incurred by the person in connection with such action, suit or proceeding, if the person acted in good faith and in a manner the person reasonably believed to be in or not opposed to the best interests of the corporation and if, with respect to any criminal action or proceeding, the person did not have reasonable cause to believe the person’s conduct was unlawful.

Section 145(b) of the DGCL provides, in general, that a corporation shall have the power to indemnify any person who was or is a party or is threatened to be made a party to any threatened, pending or completed action or suit by or in the right of the corporation to procure a judgment in its favor because the person is or was a director, officer, employee or agent of the corporation or is or was serving at the request of the corporation as a director, officer, employee or agent of any other enterprise, against any expenses (including attorneys’ fees) actually and reasonably incurred by the person in connection with the defense or settlement of such action or suit if the person acted in good faith and in a manner the person reasonably believed to be in or not opposed to the best interests of the corporation, except that no indemnification shall be made in respect of any claim, issue or matter as to which such person shall have been adjudged to be liable to the corporation unless and only to the extent that the Court of Chancery or the court in which such action or suit was brought shall determine upon application that, despite the adjudication of liability but in view of all the circumstances of the case, such person is fairly and reasonably entitled to indemnity for such expenses which the Court of Chancery or such other court shall deem proper.

18

Section 145(g) of the DGCL provides, in general, that a corporation shall have the power to purchase and maintain insurance on behalf of any person who is or was a director, officer, employee or agent of the corporation or is or was serving at the request of the corporation as a director, officer, employee or agent of any other enterprise, against any liability asserted against the person in any such capacity, or arising out of the person’s status as such, regardless of whether the corporation would have the power to indemnify the person against such liability under the provisions of the law.

Limelight’s amended and restated certificate of incorporation contains provisions that eliminate, to the maximum extent permitted by the General Corporation Law of the State of Delaware, the personal liability of directors and executive officers for monetary damages for breach of their fiduciary duties as a director or officer. Limelight’s amended and restated certificate of incorporation and bylaws provide that Limelight shall indemnify its directors and executive officers and may indemnify its employees and other agents to the fullest extent permitted by the General Corporation Law of the State of Delaware.

Limelight has entered into indemnification agreements with its directors and executive officers, in addition to the indemnification provided for in its amended and restated certificate of incorporation and bylaws.

Limelight has purchased and intends to maintain insurance on behalf of any person who is or was a director or officer of Limelight against any loss arising from any claim asserted against him or her and incurred by him or her in any such capacity, subject to certain exclusions.

The foregoing is only a general summary of certain aspects of Delaware law and Limelight’s certificate of incorporation, as amended, and bylaws, as amended, dealing with indemnification of directors and officers, and does not purport to be complete. It is qualified in its entirety by reference to the detailed provisions of Section 145 of the General Corporation Law of the State of Delaware, Limelight’s certificate of incorporation, as amended, and Limelight’s bylaws, as amended.

See also the undertakings set out in response to Item 17 herein.

See the Exhibit Index following the signature page.

The undersigned registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) To include any prospectus required by Section 10(a)(3) of the Securities Act;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than 20% change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective registration statement.

(iii) To include any material information with respect to the plan of distribution not previously disclosed in this registration statement or any material change to such information in this registration statement; provided, however, that paragraphs (1)(i), (1)(ii) and (1)(iii) do not apply if the information required to be included in a

19

post-effective amendment by those paragraphs is contained in periodic reports filed with or furnished to the Commission by the registrant pursuant to Section 13 or Section 15(d) of the Exchange Act that are incorporated by reference in this registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of this registration statement.

(2) That, for the purposes of determining any liability under the Securities Act, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(4) That, for purposes of determining any liability under the Securities Act, each filing of the registrant’s annual report pursuant to Section 13(a) or 15(d) of the Exchange Act (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to Section 15(d) of the Exchange Act) that is incorporated by reference in this registration statement shall be deemed to be a new registration statement relating to the securities offered herein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(5) Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the registrant pursuant to the indemnification provisions described herein, or otherwise, the registrant has been advised that in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

(6) That for purposes of determining any liability under the Securities Act, the information omitted from the form of prospectus filed as part of this registration statement in reliance upon Rule 430A and contained in a form of prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4), or 497(h) under the Securities Act shall be deemed to be part of this registration statement as of the time it was declared effective.

(7) That for the purpose of determining any liability under the Securities Act, each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

20

EXHIBIT INDEX

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized in the City of Tempe, State of Arizona, on February 7, 2018.

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints Robert Lento and Sajid Malhotra, and each of them, his or her true and lawful attorneys-in-fact and agents, each with full power of substitution and resubstitution, for him or her and in his or her name, place and stead, in any and all capacities, to sign any and all amendments, including post-effective amendments, to this registration statement, and any registration statement relating to the offering covered by this registration statement and filed pursuant to Rule 462 under the Securities Act of 1933, as amended, and to file the same, with exhibits thereto and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done, as fully to all intents and purposes as he or she might or could do in person, hereby ratifying and confirming all that each of said attorneys-in-fact and agents or their substitute or substitutes may lawfully so or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, the following persons have signed this registration statement in the capacities and on the date indicated.