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As filed with the Securities and Exchange Commission on December 8, 2016November 16, 2018

Registration No. 333-214737333-            

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549

FORM S-3
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

PLUG POWER INC.
(Exact name of Registrantregistrant as specified in its charter)

968 Albany Shaker Road
Latham, New York 12110
(518) 782-7700
(Address, Including Zip Code,including zip code, and Telephone Number, Including Area Code,telephone number, including area code, of Registrant's Principal Executive Offices)registrant's principal executive offices)

Andrew Marsh
President and Chief Executive Officer
Plug Power Inc.
968 Albany-Shaker Road
Latham, New York, 12110
(518) 782-7700

(Name, Address, Including Zip Code,address, including zip code, and Telephone Number, Including Area Code,telephone number, including area code, of Agentagent for Service)service)

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

           If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box.    o

           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, as amended, or the Securities Act, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box.    ý

           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.    o

           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.    o

           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 Commission pursuant to Rule 462(e) under the Securities Act, check the following box.    o

           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.    o

           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" and "smaller reporting company" in Rule 12b-2 of the Securities Exchange Act of 1934, as amended, or the Exchange Act.

           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 7(a)(2)(B) of the Securities Act. o

CALCULATION OF REGISTRATION FEE

(1)

There are beingThe securities registered hereunder such indeterminate numberconsist of 21,212,123 shares of the registrant's common stock, par value $0.01 per share, which are issuable upon conversion of shares of common stock and preferred stock, such indeterminate number of warrants to purchase common stock, preferred stock and/or debt securities, such indeterminate amount of debt securities and such indeterminate number of units as may be sold by the registrant from time to time, which together shall have an aggregate initial offering price not to exceed $200,000,000. Any securities registered hereunder may be sold separately or as units with the other securities registered hereunder.

(2)

This registration statement also includes an indeterminate number of securities that may be issued in primary offerings or upon exercise, conversion or exchange of any securities registered hereunder that provide for exercise, conversion or exchange, or that may be issued to prevent dilution resulting from stock splits, stock dividends or similar transactions inregistrant's Series E Convertible Preferred Stock, par value $0.01 per share. In accordance with Rule 416 under the Securities Act.

(3)

The proposed maximum offering price per unit will be determined, from time to time, byAct of 1933, as amended, this registration statement also covers an indeterminate number of additional shares of common stock of the registrant that may become issuable in connection with the issuance by the registrant of the securities registered hereunder. Such information is not required to be included pursuant to General Instruction II.D of Form S-3 under the Securities Act.any stock splits, stock dividends, recapitalizations or certain other capital adjustments.

(4)(2)

The proposed maximum aggregate offering price has been estimatedEstimated solely for the purpose of calculating the registration fee pursuant to Rule 457(o) under the Securities Act.

(5)

Calculated pursuant to Rule 457(o)457(c) under the Securities Act and previously paid.

(6)

This registration statement also relates to the rights to purchase Series A Junior Participating Cumulative Preferred Stockbased upon a $1.82 per share average of the registrant which are attached to all shares of common stock issued pursuant to the termshigh and low sale prices of the registrant's Shareholders Rights Agreement dated June 23, 2009,common stock as amended. Until the occurrence of certain prescribed events, the rights are not exercisable, are evidencedreported by the certificates for the common stock and will be transferred with and only with such common stock. Because no separate consideration is paid for the rights, the registration fee therefore is included in the fee for common stock.NASDAQ Capital Market on November 14, 2018.

           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 thatwhich specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act or until the registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

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The information in this prospectus is not complete and may be changed. Weselling stockholders may not sell or accept an offer to buy these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting offersan offer to buy these securities in any jurisdictionstate where suchthe offer or sale is not permitted.

Subject to Completion, Dated December 8, 2016November 16, 2018

PROSPECTUS

PLUG POWER INC.

$200,000,000
Common Stock
Preferred Stock
Warrants
Debt Securities
Units

        From21,212,123 Shares of Common Stock

        This prospectus relates to the potential resale from time to time we mayby the selling stockholders identified in this prospectus of some or all of the 21,212,123 shares of our common stock, par value $0.01 per share, or the securities, issuable upon conversion of our outstanding Series E Convertible Preferred Stock. The registration of the offer up to $200,000,000 of any combinationand sale of the securities describedcovered by this prospectus does not necessarily mean that any of the securities will be offered or sold by the selling stockholders.

        We will receive no proceeds from any resale of the shares of common stock by the selling stockholders, but we have agreed to pay certain registration expenses.

        Each selling stockholder identified in this prospectus either individually(which includes the selling stockholder's pledgees, donees, transferees, or other successors in units. The warrants and debt securitiesinterest) may be convertible intosell all or exercisable or exchangeable fora portion of the shares of common stock held by them and offered hereby from time to time directly or preferred stockthrough one or more underwriters, broker-dealers or agents, and the preferred stock may be convertible into or exchangeable for common stock.

        Each time we offer securities, we will provide the specific terms of the securities offered in one or more supplements to this prospectus. Wepublic or private transactions. The shares of common stock may also authorizebe sold in one or more free writing prospectuses to be provided to you in connection with these offerings. The prospectus supplement and any related free writing prospectus may also add, update or change information contained in this prospectus. You should carefully read this prospectus,transactions at fixed prices, at prevailing market prices at the applicable prospectus supplement and any related free writing prospectus, as well as any documents incorporated by reference, before buying anytime of the securities being offered.

        The securities offered by this prospectussale, at varying prices determined at the time of sale or at negotiated prices. These sales may be sold directly by us to investors, through agents designated from time to timeeffected in transactions, which may involve crosses or to orblock transactions. If the shares of common stock are sold through underwriters, or dealers on a continuous or delayed basis. We will set forth the names of any underwritersbroker-dealers or agents, and any applicable fees,the selling stockholders will be responsible for underwriting discounts or commissions discounts and over-allotments in an accompanying prospectus supplement. For additional information on the methods of sale, you should refer toor agent's commissions. See the section entitled "Plan of Distribution" infor more information about how the selling stockholders will sell the shares of common stock being registered pursuant to this prospectus and in the applicable prospectus supplement. The price to the public of such securities and the net proceeds we expect to receive from such sale will also be set forth in a prospectus supplement.prospectus.

        Our common stock is traded on the NASDAQ Capital Market under the symbol "PLUG." On November 17, 2016,15, 2018, the last reported sale price of our common stock on the NASDAQ Capital Market was $1.51. The applicable prospectus supplement will contain information, where applicable, as to any other listing, if any, on the NASDAQ Capital Market or any securities market or other exchange of the securities covered by the applicable prospectus supplement.$1.84 per share.

        ThisInvesting in our securities involves a high degree of risk. You should review carefully the risks and uncertainties referenced under the heading "Risk Factors" on page 4 of this prospectus may not be used to offer or sell any securities unless accompaniedand under similar headings in the other documents that are incorporated by a prospectus supplement.

INVESTING IN OUR SECURITIES INVOLVES A HIGH DEGREE OF RISK. YOU SHOULD REVIEW CAREFULLY THE RISKS AND UNCERTAINTIES REFERENCED UNDER THE HEADING "RISK FACTORS" ON PAGE 6 OF THIS PROSPECTUS AS WELL AS THOSE CONTAINED IN THE APPLICABLE PROSPECTUS SUPPLEMENT AND ANY RELATED FREE WRITING PROSPECTUS, AND IN THE OTHER DOCUMENTS THAT ARE INCORPORATED BY REFERENCE INTO THIS PROSPECTUS OR THE APPLICABLE PROSPECTUS SUPPLEMENT.reference into this prospectus.

        Neither the Securities and Exchange Commission, or SEC, nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is                , 2016.2018.

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ABOUT THIS PROSPECTUS

        This prospectus is part of a shelf registration statement on Form S-3 that we filed with the Securities and Exchange Commission, or the SEC, utilizing a "shelf" registration process.SEC. Under this shelf registration, process, wethe selling stockholders may offerfrom time to time sell the shares of our common stock and preferred stock, various series of warrants to purchase common stock or preferred stock and debt securities, either individually ordescribed in units,this prospectus in one or more offerings, upofferings. When a selling stockholder elects to a total dollar amountmake an offer of $200,000,000. This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities undercommon stock pursuant to this prospectus, we will provideregistration statement, a prospectus supplement, if required, may be distributed that will contain more specific information about the specific terms of thethat offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. Each suchAny required prospectus supplement (and any related free writing prospectus that we may authorize to be provided to you) may also add, update or change information contained in this prospectus or in documents incorporated by reference into this prospectus. We urge you to carefullyYou should read both this prospectus and any applicable prospectus supplement and any related free writing prospectus, together with theadditional information incorporated herein by reference as described below under the headingsheading "Where You Can Find Additional Information" and "Incorporation of Certain Information by Reference" before buying any of the securities being offered.

This prospectus may not be used to offer or sell securities unless it is accompanied by a prospectus supplement.

        You should rely only on the information contained or incorporated by reference in this prospectus, any applicable prospectus supplement and any related free writing prospectus. WeNeither we nor the selling stockholders have not authorized anyone to provide you with different information in addition to or different from that contained in this prospectus, any applicable prospectus supplement and any related free writing prospectus. No dealer, salesperson or other person is authorized to give any information or to represent anything not contained in this prospectus, any applicable prospectus supplement or any related free writing prospectus that we may authorize to be provided to you. You must not rely on any unauthorized information or representation. This prospectus is an offer to sell only the securities offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so. You should assume that the information in this prospectus and any applicable prospectus supplement oris accurate only as of the date on its respective cover, that the information appearing in any related free writing prospectus is accurate only as of the date on the front of the documentthat free writing prospectus, and that any information incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus, any applicable prospectus supplement or any related free writing prospectus, or any sale of a security. Our business, financial condition, results of operations and prospects may have changed since those dates.

        This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which this prospectus is a part, and you may obtain copies of those documents as described below under the heading "Where You Can Find Additional Information."

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INCORPORATION OF CERTAIN INFORMATION BY REFERENCE

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RISK FACTORS

        Investing in our securities involves a high degree of risk. Before purchasing our securities, you should carefully consider the risks and uncertainties set forth under the heading "Risk Factors" in our Annual Report on Form 10-K for the fiscal year ended December 31, 2015, filed with the SEC on March 14, 2016,2017 and our quarterly reportsQuarterly Reports on Form 10-Q for the quartersperiods ended March 31, 2015,2018, June 30, 20152018 and September 30, 2016, filed on May 10, 2016, August 9, 2016 and November 8, 2016, respectively,2018, each of which areis incorporated by reference in this prospectus, as well as any updates theretotogether with other information contained in subsequent filings withthis prospectus, and the SEC orinformation and documents incorporated by reference in this prospectus, any applicable prospectus supplement or free writing prospectus. If any of these risks were to occur, our business, financial condition or results of operations would likely suffer. In that event, the value of our securities could decline, and you could lose all or part of your investment. The risks and uncertainties we describe are not the only ones facing us.we face. Additional risks not presently known to us or that we currently deem immaterial may also impair our business operations and the markettrading price of our securities or the value of your investment.common stock.

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

        This prospectus contains statements that are not historical facts and are considered forward-looking within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act. These forward-looking statements contain projections of our future results of operations or of our financial position or state other forward-looking information. In some cases you can identify these statements by forward-looking words such as "anticipate," "believe," "could," "continue," "estimate," "expect," "intend," "may," "should," "will," "would," "plan," "projected" or the negative of such words or other similar words or phrases. We believe that it is important to communicate our future expectations to our investors. However, there may be events in the future that we are not able to accurately predict or control and that may cause our actual results to differ materially from the expectations we describe in our forward-looking statements. Investors are cautioned not to unduly rely on forward-looking statements because they involve risks and uncertainties, and actual results may differ materially from those discussed as a result of various factors, including, but not limited to: the risk that we continue to incur losses and might never achieve or maintain profitability;anticipate continuing to incur losses; the risk that we will need to raise additional capital to fund our operations and such capital may not be available to us; the risk of dilution to our stockholders and/or stock price should we need to raise additional capital; the risk that our lack of extensive experience in manufacturing and marketing products may impact our ability to manufacture and market products on a profitable and large-scale commercial basis; the risk that unit orders will not ship, be installed and/or converted to revenue, in whole or in part; the risk that a loss of one or more of our major customers could result in a material adverse effect on our financial condition; the risk that a sale of a significant number of shares of stock could depress the market price of our common stock; the risk that negative publicity related to our business or stock could result in a negative impact on our stock value and profitability; the risk of potential losses related to any product liability claims or contract disputes; the risk of loss related to an inability to maintain an effective system of internal controls; our ability to attract and maintain key personnel; the risks related to the use of flammable fuels in our products; the risk that pending orders may not convert to purchase orders, in whole or in part; the cost and timing of developing, marketing and selling our products and our ability to raise the necessary capital to fund such costs; our ability to obtain financing arrangements to support the sale or leasing of our products and services to customers; the ability to achieve the forecasted gross margin on the sale of our products;products and services; the volatility of our stock price; the risk that a sale of a significant number of shares of stock could depress the market price of our common stock; the risk that a loss of one or more of our major customers could result in a material adverse effect on our financial condition; the cost and availability of fuel and fueling infrastructures for our products; the risk of elimination of government subsidies and economic incentives for alternative energy products; market acceptancethe risk of potential losses related to any product liability claims or contract disputes; competitive factors, such as price competition and competition from other traditional and alternative energy companies; the cost and availability of components and parts for our products and services, including GenDrive units;products; our ability to establish and maintain relationships with third parties with respect to product development, manufacturing, distribution and servicing and the supply of key product components; the risk that pending orders may not convert to purchase orders, in whole or in part; the risk that unit orders will not ship, be installed and/or converted to revenue, in whole or in part; the risks related to the use of flammable fuels in our products; our ability to protect our intellectual property; the risk that our lack of extensive experience in manufacturing and marketing products may impact our ability to manufacture and market products on a profitable and large-scale commercial basis; the cost and availabilitytiming of componentsdeveloping, marketing and parts forselling our products;products and our ability to raise the necessary capital to fund such costs; market acceptance of our products and services, including GenDrive units; our ability to develop commercially viable products; our ability to reduce product and manufacturing costs; our ability to

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successfully market, distribute and service our products and services internationally; our ability to improve system reliability for our products; competitive factors, such as price competition and competition from other traditional and alternative energy companies;

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the risk of loss related to our inability to maintain an effective system of internal controls; our ability to protect our intellectual property;attract and maintain key personnel; the risks associated with potential future acquisitions; the cost of complying with current and future federal, state and international governmental regulations; the risks associated with potential future acquisitions; the volatility of our stock price; and other risks and uncertainties referenceddiscussed under "Risk Factors" above and in any applicable prospectus supplement or free writing prospectus and any documents incorporated by reference herein or therein. Readers should not place undue reliance on our forward-looking statements. These forward-looking statements speak only as of the date on which the statements were made and are not guarantees of future performance. Except as may be required by applicable law, we do not undertake or intend to update any forward-looking statements after the date of this prospectus or the respective dates of documents incorporated herein or therein that include forward-looking statements.

ABOUT THE COMPANY

        We are a leading provider of alternative energy technology focused on the design, development, commercialization and manufacture of hydrogen and fuel cell systems used primarily for the electric mobility and stationary power markets. As part of the global drive to electrification, we have recently leveraged product proven in the material handling vehicle space to enter new, adjacent, electric vehicle markets, specifically electric delivery vans.

        We are focused on proton exchange membrane, or PEM, fuel cell and fuel processing technologies, fuel cell/battery hybrid technologies, and associated hydrogen storage and dispensing infrastructure from which multiple products are available. A fuel cell is an electrochemical device that combines hydrogen and oxygen to produce electricity and heat without combustion. Hydrogen is derived from hydrocarbon fuels such as liquid petroleum gas, propane, methanol, ethanol, gasoline or biofuels. We develop complete hydrogen generation, delivery, storage and refueling solutions for customer locations. Currently, we obtain the majority of our hydrogen by purchasing it from fuel suppliers for resale to customers.

        In our core business, we provide and continue to develop commercially-viable hydrogen and fuel cell product solutions to replace lead-acid batteries in electric material handling vehicles and industrial trucks for some of the world's largest retail-distribution and manufacturing businesses. We are focusing our efforts on industrial mobility applications (electric forklifts and electric industrial vehicles) at multi-shift high volume manufacturing and high throughput distribution sites where our products and services provide a unique combination of productivity, flexibility and environmental benefits. Additionally, we manufacture and sell fuel cell products to replace batteries and diesel generators in stationary backup power applications. These products prove valuable with telecommunications, transportation and utility customers as robust, reliable and sustainable power solutions.

        Our current products and services include:

GenDrive: GenDrive is our hydrogen fueled PEM fuel cell system providing power to material handling electric vehicles, including class 1, 2, 3 and 6 electric forklifts and ground support equipment.

GenFuel: GenFuel is our hydrogen fueling delivery, generation, storage and dispensing systems.

GenCare: GenCare is our ongoing 'internet of things'-based maintenance and on-site service program for GenDrive fuel cells, GenSure products, GenFuel products and ProGen engines.

GenSure: GenSure is our stationary fuel cell solution providing scalable, modular PEM fuel cell power to support the backup and grid-support power requirements of the telecommunications, transportation, and utility sectors.

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GenKey: GenKey is our turn-key solution combining either GenDrive or GenSure power with GenFuel fuel and GenCare aftermarket service, offering complete simplicity to customers transitioning to fuel cell power.

ProGen: ProGen is our fuel cell stack and engine technology currently used globally in mobility and stationary fuel cell systems, and as engines in electric delivery vans.

        We provide our products worldwide through our direct product sales force, and by leveraging relationships with original equipment manufacturers and their dealer networks. We manufacture our commercially-viable products in Latham, NY.

        We were organized in the State of Delaware on June 27, 1997.

        Our principal executive offices are located at 968 Albany-Shaker Road, Latham, New York, 12110, and our telephone number is (518) 782-7700. Our corporate website address iswww.plugpower.com. Information on our website is not deemed to be a part of this prospectus or any applicable prospectus supplement. Our common stock trades on the NASDAQ Capital Market under the symbol "PLUG."

ABOUT THE OFFERING

        This prospectus relates to the potential resale from time to time by the selling stockholders identified in this prospectus of some or all of the 21,212,123 shares of our common stock, par value $0.01 per share, issuable upon conversion of outstanding shares of Series E Convertible Preferred Stock. We agreed to file a registration statement to register the resale of such shares of common stock in connection with our issuance of the shares of Series E Convertible Preferred Stock. See "Use of Proceeds," "Selling Stockholders" and "Plan of Distribution" for additional information concerning this offering.

USE OF PROCEEDS

        This prospectus relates to the shares of our common stock that may be offered and sold from time to time by the selling stockholders who will receive all of the proceeds from any sale of such shares. We will not receive any proceeds from any sales of shares of our common stock by the selling stockholders.

SELLING STOCKHOLDERS

        On November 2, 2018, we entered into that certain Registration Rights Agreement with Tech Opportunities LLC and CVI Investments, Inc., pursuant to which we agreed, among other things, to (i) file as soon as practicable a registration statement with the SEC covering the resale of the shares of common stock issuable upon conversion of the Series E Convertible Preferred Stock and (ii) use our reasonable best efforts to have such registration statement declared effective by the SEC as soon as practicable. The registration statement of which this prospectus forms a part is being filed to satisfy our obligations under the Registration Rights Agreement.

        When we refer to the "selling stockholders" in this prospectus, we mean the stockholders listed in the table below and its pledgees, donees, transferees or other successors in interest.

        The following table sets forth:

•

the number of shares of common stock beneficially owned by the selling stockholders prior to the sale of the shares of common stock covered by this prospectus;



•

the number of shares of common stock that may be offered for sale by the selling stockholders pursuant to this prospectus;

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the number of shares of common stock to be beneficially owned by the selling stockholders following the sale of any shares of common stock covered by this prospectus; and



•

the percentage of our issued and outstanding shares of common stock beneficially owned by the selling stockholders prior to and following the sale of all shares of common stock covered by this prospectus.

        All information with respect to common stock ownership of the selling stockholders has been furnished by or on behalf of the selling stockholders and is as of November 16, 2018.

        Beneficial ownership for the purposes of the table below is determined in accordance with the rules and regulations of the SEC. These rules generally provide that a person is the beneficial owner of securities if such person has or shares the power to vote or direct the voting thereof, or to dispose or direct the disposition thereof or has the right to acquire such powers within 60 days. We believe, based on information supplied by the selling stockholders, that except as may otherwise be indicated in the table below, the selling stockholders have sole voting and dispositive power with respect to the common stock reported as beneficially owned by them.

        Because the selling stockholders are not obligated to sell the shares of common stock, we cannot estimate the amount of the shares of common stock that the selling stockholders will hold upon consummation of any such sales. For purposes of the following table, we have assumed the sale of all of the shares of common stock that may be offered for sale pursuant to this prospectus.

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RATIO OF COMBINED FIXED CHARGES AND PREFERENCE DIVIDENDS TO EARNINGS

        Our ratio of combined fixed charges and preference dividends to earnings for each of the five most recently completed fiscal years and any required interim periods will each be specified in a prospectus supplement or in a document that we file with the SEC and incorporate by reference pertaining to the issuance, if any, by us of debt securities and/or preference securities in the future.

USE OF PROCEEDS

        Except as described in any prospectus supplement or in any related free writing prospectus that we may authorize to be provided to you, the net proceeds received by us from our sale of the securities described in this prospectus will be added to our general funds and will be used for our general corporate purposes. From time to time, we may engage in additional public or private financings of a character and amount which we may deem appropriate.

PLAN OF DISTRIBUTION

        We may sellare registering the securitiesshares of common stock issuable upon conversion of the Series E Convertible Preferred Stock to permit the resale of these shares of common stock by the selling stockholders from time to time pursuantafter the date of this prospectus. We will not receive any of the proceeds from the sale by the selling stockholders of the shares of common stock. We will bear all fees and expenses incident to underwritten public offerings, negotiated transactions, block tradesour obligation to register the shares of common stock.

        The selling stockholders may sell all or a combinationportion of these methods. We may sell the securitiesshares of common stock held by them and offered hereby from time to time directly or through one or more underwriters, broker-dealers or dealers,agents. If the shares of common stock are sold through underwriters, broker-dealers, or agents remarketing firmsthe selling stockholders will be responsible for underwriting discounts or other third parties and/commissions or directlyagent's commissions. The shares of common stock may be sold in one or more transactions at fixed prices, at prevailing market prices at the time of the sale, at varying prices determined at the time of sale or at negotiated prices. These sales may be effected in transactions, which may involve crosses or block transactions, pursuant to one or more purchasers. In some cases, we or dealers acting with us or on our behalf may also purchase our securities and reoffer them toof the public. We may also offer and sell, or agree to deliver, our securities pursuant to, or in connection with, any option agreement or other contractual arrangement. We may distribute securities from time to time in one or more transactions:following methods:

•

at a fixed priceon any national securities exchange or prices,quotation service on which the securities may be changed;



•

at market prices prevailinglisted or quoted at the time of sale;



•

at prices related to such prevailing market prices; or



•

at negotiated prices.

        Each time we offer and sell securities, we will provide a prospectus supplement that will set forthin the terms of the offering of the securities, including:

•

the name or names of the underwriters, if any;over-the-counter market;



•

in transactions otherwise than on these exchanges or systems or in the purchase price of the securities and the proceeds we will receive from the sale;over-the-counter market;



•

any over-allotmentthrough the writing or othersettlement of options, under which underwriters may purchase additional securities;whether such options are listed on an options exchange or otherwise;



•

any agency fees or underwriting discountsordinary brokerage transactions and other items constituting agents' or underwriters' compensation;transactions in which the broker-dealer solicits purchasers;



•

any public offering price;block trades in which the broker-dealer will attempt to sell the shares as agent but may position and resell a portion of the block as principal to facilitate the transaction;



•

purchases by a broker-dealer as principal and resale by the broker-dealer for its account;



•

an exchange distribution in accordance with the rules of the applicable exchange;



•

privately negotiated transactions;



•

short sales made after the date the registration statement is declared effective by the SEC;



•

broker-dealers may agree with a selling security holder to sell a specified number of such shares at a stipulated price per share;



•

a combination of any discounts or concessions allowed or reallowed or paid to dealers;such methods of sale; and



•

any securities exchangeother method permitted pursuant to applicable law.

        The selling stockholders may also sell shares of common stock under Rule 144 promulgated under the Securities Act, if available, rather than under this prospectus. In addition, the selling stockholders may transfer the shares of common stock by other means not described in this prospectus. If the selling stockholders effect such transactions by selling shares of common stock to or market on whichthrough underwriters, broker-dealers or agents, such underwriters, broker-dealers or agents may receive commissions in the securitiesform of discounts, concessions or commissions from the selling stockholders or commissions from purchasers of the shares of common stock for whom they may act as agent or to whom they may sell as principal (which discounts, concessions or commissions as to particular underwriters, broker-dealers or agents may be listed.

        If underwriters are usedin excess of those customary in the sale, they will acquire the securities for their own account and may resell the securities from time to time in one or moretypes of transactions at a fixed public offering price or at varying prices determined at the time of sale. The obligationsinvolved). In connection with sales of the underwriters to purchaseshares of common stock or otherwise, the securities will be subject toselling stockholders may enter into hedging transactions with broker-dealers, which may in turn engage in short sales of the conditions set forthshares of common stock in the applicable underwriting agreement. Wecourse of hedging in positions they assume. The selling stockholders may offer the securities to the public through underwriting syndicates represented by managing underwriters or by underwriters without a syndicate. If applicable, we will include the names of the specific managing underwriter or underwriters, as well as the names of any other underwriters, and the termsalso sell shares of

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the transactions, including the compensation the underwriterscommon stock short and dealers will receive,deliver shares of common stock covered by this prospectus to close out short positions and to return borrowed shares in the applicable prospectus supplement. Subjectconnection with such short sales. The selling stockholders may also loan or pledge shares of common stock to certain conditions, the underwriters will be obligated to purchasebroker-dealers that in turn may sell such shares.

        The selling stockholders may pledge or grant a security interest in some or all of the securities offeredSeries E Convertible Preferred Stock or shares of common stock owned by them and, if they default in the performance of their secured obligations, the pledgees or secured parties may offer and sell the shares of common stock from time to time pursuant to this prospectus or any amendment to this prospectus under Rule 424(b)(3) or other applicable provision of the Securities Act amending, if necessary, the list of selling stockholders to include the pledgee, transferee or other successors in interest as selling stockholders under this prospectus. The selling stockholders also may transfer and donate the shares of common stock in other circumstances in which case the pledgees, transferees, donees, or other successors in interest will be the selling beneficial owners for purposes of this prospectus.

        To the extent required by the prospectus supplement, other than securities covered bySecurities Act and the rules and regulations thereunder, the selling stockholders and any over-allotment optionbroker-dealer participating in the distribution of the shares of common stock may be deemed to be "underwriters" within the meaning of the Securities Act, and any commission paid, or option to purchase additional securities. Any public offering price and any discounts or concessions allowed or reallowed or paid to, dealers may change from time to time. We may use underwriters with whom we or they have a material relationship. The prospectus supplement, naming the underwriter, will describe the nature of any such relationship.

        We may sell securities directly or through agents we or they designate from time to time. The prospectus supplement will name any agent involved in the offering and sale of securities and any commissions we will pay to them. Unless the prospectus supplement states otherwise, any agent will be acting on a best-efforts basis for the period of its appointment. Agentsbroker-dealer may be deemed to be underwritersunderwriting commissions or discounts under the Securities Act, of any of our securities that they offer or sell.

        We may use a dealer to sell our securities. If we use a dealer, we will sell our securities to the dealer, as principal. The dealer will then sell our securities to the public at varying prices that the dealer will determine atAct. At the time it sells our securities. We will include the namea particular offering of the dealershares of common stock is made, a prospectus supplement, if required, will be distributed, which will set forth the aggregate amount of shares of common stock being offered and the terms of the transactions withoffering, including the dealername or names of any broker-dealers or agents, any discounts, commissions and other terms constituting compensation from the selling stockholders and any discounts, commissions or concessions allowed or re-allowed or paid to broker-dealers.

        Under the securities laws of some states, the shares of common stock may be sold in such states only through registered or licensed brokers or dealers. In addition, in some states the shares of common stock may not be sold unless such shares have been registered or qualified for sale in such state or an exemption from registration or qualification is available and is complied with.

        There can be no assurance that any selling stockholder will sell any or all of the shares of common stock registered pursuant to the registration statement, of which this prospectus forms a part.

        The selling stockholders and any other person participating in such distribution will be subject to applicable provisions of the Exchange Act and the rules and regulations thereunder, including, without limitation, to the extent applicable, Regulation M of the Exchange Act, which may limit the timing of purchases and sales of any of the shares of common stock by the selling stockholders and any other participating person. To the extent applicable, Regulation M may also restrict the ability of any person engaged in the applicable prospectus supplement.distribution of the shares of common stock to engage in market-making activities with respect to the shares of common stock. All of the foregoing may affect the marketability of the shares of common stock and the ability of any person or entity to engage in market-making activities with respect to the shares of common stock.

        We may authorize agents or underwriters to solicit offers by certain purchasers to purchase securities from us or them atwill pay all expenses of the public offering price set forth inregistration of the prospectus supplementshares of common stock pursuant to delayed delivery contracts providing for paymentthe registration rights agreement, estimated to be approximately $79,680, including, without limitation, SEC filing fees; provided, however, a selling stockholder will pay all underwriting discounts and delivery on a specified date inselling commissions, if any. We will indemnify the future. The prospectus supplement will set forthselling stockholders against liabilities, including some liabilities under the conditions to these contracts and any commissions we must pay for solicitation of these contracts.

        We may effect sales of securities in connection with forward sale, option or other types of agreements with third parties. Any distribution of securities pursuant to any forward sale agreement may be effected from time to time in one or more transactions that may take place through a stock exchange, including block trades or ordinary broker's transactions, or through broker-dealers acting either as principal or agent, or through privately-negotiated transactions, or through an underwritten public offering, or through a combination of any such methods of sale, at market prices prevailing at the time of sale, prices relating to such prevailing market prices or at negotiated or fixed prices.

        We may engage in at the market offerings into an existing trading marketSecurities Act in accordance with Rule 415(a)(4) under the Securities Act.

registration rights agreements or the selling stockholders will be entitled to contribution. We may provide agents and underwriters with indemnificationbe indemnified by the selling stockholders against civil liabilities, including liabilities under the Securities Act or contribution with respectthat may arise from any written information furnished to payments thatus by the agents or underwriters may make with respect to these liabilities. Agents and underwriters may engageselling stockholder specifically for use in transactions with, or perform services for, us in the ordinary course of business.

        All securities we may offer, other than common stock, will be new issues of securities with no established trading market. Any underwriters may make a market in these securities, but will not be obligated to do so and may discontinue any market making at any time without notice. We cannot guarantee the liquidity of the trading markets for any securities.

        Any underwriter may engage in over-allotment, stabilizing transactions, short-covering transactions and penalty bidsthis prospectus, in accordance with Regulation M under the Exchange Act. Over-allotment involves sales in excess of the offering size, which create a short position. Stabilizing transactions permit bidsrelated registration rights agreements or we may be entitled to purchase the underlying security so long as the stabilizing bids do not exceed a specified maximum price. Syndicate-covering or other short-covering transactions involve purchases of the securities, either through exercise of the over-allotment option or in the open market after the distribution is completed, to cover short positions. Penalty bids permit the underwriters to reclaim a selling concession from a dealer when the securities originally sold by the dealer are purchased in a stabilizing or covering transaction to cover short positions. Those activities may cause the price of the securities to be highercontribution.

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than it would otherwise be. If commenced,        We will not receive any proceeds from sales of any shares of common stock by the underwriters may discontinueselling stockholders.

        We cannot assure you that the selling stockholders will sell all or any portion of the activities at any time.

        Any underwriters that are qualified market makers onshares of common stock offered hereby. Once sold under the NASDAQ Capital Market may engage in passive market making transactionsregistration statement, of which this prospectus forms a part, the shares of common stock will be freely tradable in the common stock onhands of persons other than our affiliates.

        To the NASDAQ Capital Marketextent permitted by applicable law, this plan of distribution may be modified in accordance with Regulation M under the Exchange Act, during the business day prior to the pricinga prospectus supplement or otherwise. All of the offering, beforeforegoing may affect the commencement of offers or sales of the common stock. Passive market makers must comply with applicable volume and price limitations and must be identified as passive market makers. In general, a passive market maker must display its bid at a price not in excess of the highest independent bid for such security; if all independent bids are lowered below the passive market maker's bid, however, the passive market maker's bid must then be lowered when certain purchase limits are exceeded. Passive market making may stabilize the market price of the securities at a level above that which might otherwise prevail in the open market and, if commenced, may be discontinued at any time.

        In compliance with guidelines of the Financial Industry Regulatory Authority, or FINRA, the maximum consideration or discount to be received by any FINRA member or independent broker dealer may not exceed 8% of the aggregate amountmarketability of the securities offered pursuant to this prospectus and any applicable prospectus supplement.

        The specific terms of the lock-up provisions, if any, in respect of any given offering will be described in the applicable prospectus supplement.hereby.

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DESCRIPTION OF CAPITAL STOCK

        This section describes the general terms of our common stock and preferred stock that we may offer from time to time. For more detailed information, a holder of our common stock and/or preferred stock should refer to our amended or restated certificate of incorporation (as amended), which we refer to herein as our certificate of incorporation, our by-lawsamended and restated bylaws, which we refer to herein as our bylaws, and our shareholder rights agreement with respect to our preferred share purchase rights, copies of which are filed with the SEC as exhibits to the registration statement of which this prospectus is a part.

General

        Our authorized capital stock consists of 450,000,000750,000,000 shares of common stock, $0.01 par value $0.01 per share, and 5,000,000 shares of preferred stock, $0.01 par value $0.01 per share. As of November 18, 2016,16, 2018, there were 180,610,344233,386,094 shares of our common stock outstanding, and 5,2312,620 shares of our Series C Redeemable Convertible Preferred Stock ("Series C Preferred Stock") outstanding, and 35,000 shares of our Series E Convertible Preferred Stock ("Series E Preferred Stock") outstanding.

        The following summary description of our capital stock is based on the provisions of our amended and restated certificate of incorporation and amended and restated bylaws and the applicable provisions of the Delaware General Corporation Law. This information is qualified entirely by reference to the applicable provisions of our amended and restated certificate of incorporation amended and restated bylaws and the Delaware General Corporation Law. For information on how to obtain copies of our amended and restated certificate of incorporation and amended and restated bylaws, which are exhibits to the registration statement of which this prospectus is a part, see "Where You Can Find Additional Information" and "Incorporation of Certain Information by Reference."

Common Stock

        Holders of shares of our common stock are entitled to one vote for each share held of record on all matters to be voted on by stockholders, including the election of directors. Our amended and restated certificate of incorporation and amended and restated bylaws do not provide for cumulative voting rights. Because of this, the holders of a majority of our common stock entitled to vote in any election of directors can elect all of the directors standing for election. Subject to the preferences that may be applicable to any then outstanding preferred stock (including the Series C Preferred Stock and Series E Preferred Stock), the holders of our outstanding shares of common stock are entitled to receive dividends, if any, as may be declared from time to time by our board of directors out of legally available funds. In the event of our liquidation, dissolution or winding up, holders of our 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, subject to the satisfaction of any liquidation preference granted to the holders of any outstanding shares of preferred stock (including the Series C Preferred Stock and Series E Preferred Stock). Holders of our common stock have no preemptive, conversion or subscription rights, and there are no redemption or sinking fund provisions applicable to our common stock. The rights, preferences and privileges of the holders of our common stock are subject to, and may be adversely affected by, the rights of the holderholders of our Series C Preferred Stock as well as the rightsshares of any series of our preferred stock that we may designate and issue in the future.

Preferred Stock

        Pursuant to our amended and restated certificate of incorporation, our board of directors has the authority, without further action by the stockholders (unless such stockholder action is required by applicable law or NASDAQ rules), to designate and issue up to 5,000,000 shares of preferred stock in one or more series, to establish from time to time the number of shares to be included in each such series, to fix the rights, preferences and privileges of the shares of each wholly unissued series, and any qualifications,

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limitations or restrictions thereon, and to increase or decrease the number of shares of any such series, but not below the number of shares of such series then outstanding.

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        We will fix the rights, preferences and privileges of the preferred stock of each such series, as well as any qualifications, limitations or restrictions thereon, in the certificate of designation relating to that series. We will file as an exhibit to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC the form of any certificate of designation that describes the terms of the series of preferred stock we are offering before the issuance of that series of preferred stock. This description will include:

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the title and stated value;



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the number of shares we are offering;



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the liquidation preference per share;



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the purchase price;



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the dividend rate, period and payment date and method of calculation for dividends;



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whether dividends will be cumulative or non-cumulative and, if cumulative, the date from which dividends will accumulate;



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the procedures for any auction and remarketing, if any;



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the provisions for a sinking fund, if any;



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the provisions for redemption or repurchase, if applicable, and any restrictions on our ability to exercise those redemption and repurchase rights;



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any listing of the preferred stock on any securities exchange or market;



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whether the preferred stock will be convertible into our common stock, and, if applicable, the conversion price, or how it will be calculated, and the conversion period;



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whether the preferred stock will be exchangeable into debt securities, and, if applicable, the exchange price, or how it will be calculated, and the exchange period;



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voting rights, if any, of the preferred stock;



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preemptive rights, if any;



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restrictions on transfer, sale or other assignment, if any;



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whether interests in the preferred stock will be represented by depositary shares;



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a discussion of any material United States federal income tax considerations applicable to the preferred stock;



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the relative ranking and preferences of the preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs;



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any limitations on the issuance of any class or series of preferred stock ranking senior to or on a parity with the series of preferred stock as to dividend rights and rights if we liquidate, dissolve or wind up our affairs; and



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any other specific terms, preferences, rights or limitations of, or restrictions on, the preferred stock.

        The General Corporation Law of the State of Delaware, the state of our incorporation, provides that the holders of preferred stock will have the right to vote separately as a class (or, in some cases, as a series) on an amendment to our amended and restated certificate of incorporation if the amendment would change the par value, the number of authorized shares of the class or the powers, preferences or special rights of the

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class or series so as to adversely affect the class or series, as the case may be. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

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        Our board of directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of our common stock. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deferring or preventing a change in our control and may adversely affect the market price of the common stock and the voting and other rights of the holders of common stock. Additionally, the issuance of preferred stock may have the effect of decreasing the market price of our common stock.

Series C Redeemable Convertible Preferred Stock

        The Series C Preferred Stock votes together with the common stock on an as-converted basisas a single class on all matters, including the election of directors, except as otherwise required by law. Each share of Series C Preferred Stock is entitled to a number of votes equal to the number of whole shares of common stock into which such share of Series C Preferred Stock is convertible.convertible (calculated by aggregating all shares of Series C Preferred Stock held by each record holder and rounding the number of shares of common stock issuable upon their conversion down to the nearest whole share).

        The Series C Preferred Stock ranks senior to the common stock and the Series E Preferred Stock with respect to rights upon the liquidation, dissolution or winding up of our company. Thethe Company. In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company, or other deemed liquidation event, each share of Series C Preferred Stock will be entitled to be paid an amount equal to the greater of (i) the original issue price of $248.794, plus any accrued but unpaid dividends or (ii) the amount that would have been payable if such share of Series C Preferred Stock had been converted to shares of common stock immediately prior to such liquidation event. Each share of Series C Preferred Stock is entitled to receive dividends at a rate of 8% per annum, based upon the original issue price of $248.794, payable in equal quarterly installments in cash or in shares of common stock, at our option. The Series C Preferred Stock is convertible into shares of common stock, at a conversion price equal to $0.2343 per share (as of November 17, 20169, 2018, and subject to future adjustments). As of November 17, 2016,9, 2018, the outstanding shares of our Series C Preferred Stock arewere convertible into an aggregate of 5,554,5942,782,075 shares of our common stock. The Series C Preferred Stock has customary redemption rights at the election of either us or the holder thereof as well as weighted average anti-dilution protection.

Series E Convertible Preferred Stock

        The Series E Preferred Stock has no voting rights, except as otherwise required by law. The Series E Preferred Stock ranks senior to the common stock with respect to rights upon the liquidation, dissolution or winding up of the Company. In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company, or other deemed liquidation event, each share of Series E Preferred Stock will be entitled to be paid an amount, after any amount that is required to be paid to the holders of Series C Preferred Stock, equal to the greater of (i) 125% of the applicable conversion amount of the Series E Preferred Stock on such date or (ii) the amount that would have been payable if such share of Series E Preferred Stock had been converted to shares of common stock immediately prior to such liquidation event. Each share of Series E Preferred Stock is convertible into $1,000 worth of shares of common stock, at a conversion price equal to $2.31 per share (as of November 16, 2018, and subject to adjustment under certain conditions). The Company is required to redeem the Series E Preferred Stock for cash (or, subject to certain conditions, at the Company's option, in common stock or a combination of cash and common stock) in thirteen monthly installments of $2.693 million each from May 2019 through May 2020. Common stock used for redemptions will generally be valued based on a discounted VWAP formula. As of November 16, 2018, the outstanding shares of our Series E Preferred Stock were convertible into an aggregate of 15,151,516 shares of our common stock.

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Delaware Anti-Takeover Law and Provisions of our Amended and Restated Certificate of Incorporation and Amended and Restated Bylaws

        Delaware Anti-Takeover Law.    We are subject to Section 203 of the Delaware General Corporation Law. Section 203 generally prohibits a public Delaware corporation from engaging in a "business combination" with an "interested stockholder" for a period of three years after the date of the transaction in which the person became an interested stockholder, unless:

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prior to the date of the transaction, the board of directors of the corporation approved either the business combination or the transaction which resulted in the stockholder becoming an interested stockholder;



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the interested stockholder owned at least 85% of the voting stock of the corporation outstanding at the time the transaction commenced, excluding for purposes of determining the number of shares outstanding (a) shares owned by persons who are directors and also officers and (b) shares owned by employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer; or



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on or subsequent to the date of the transaction, the business combination is approved by the board and authorized at an annual or special meeting of stockholders, and not by written consent, by the affirmative vote of at least 66-2/3%66²/3% of the outstanding voting stock which is not owned by the interested stockholder.

Section 203 defines a business combination to include:

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any merger or consolidation involving the corporation and the interested stockholder;



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any sale, transfer, pledge or other disposition involving the interested stockholder of 10% or more of the assets of the corporation;

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subject to exceptions, any transaction that results in the issuance or transfer by the corporation of any stock of the corporation to the interested stockholder; and



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the receipt by the interested stockholder of the benefit of any loans, advances, guarantees, pledges or other financial benefits provided by or through the corporation.

        In general, Section 203 defines an interested stockholder as any entity or person beneficially owning 15% or more of the outstanding voting stock of the corporation or any entity or person affiliated with or controlling or controlled by the entity or person.

        Amended and Restated Certificate of Incorporation and Amended and Restated Bylaws.    Provisions of our amended and restated certificate of incorporation and amended and restated bylaws may delay or discourage transactions involving an actual or potential change in our control or change in our management, including transactions in which stockholders might otherwise receive a premium for their shares or transactions that our stockholders might otherwise deem to be in their best interests. Therefore, these provisions could adversely affect the price of our common stock. Among other things, our amended and restated certificate of incorporation and amended and restated bylaws:

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permit our board of directors to issue up to 5,000,000 shares of preferred stock, with any rights, preferences and privileges as they may designate;



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provide that the authorized number of directors may be changed only by resolution of the board of directors;



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provide that all vacancies, including newly created directorships, may, except as otherwise required by law and subject to the rights of the holders of any series of preferred stock, be filled by the affirmative vote of a majority of directors then in office, even if less than a quorum;



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divide our board of directors into three classes;