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The information in this prospectus is not complete and may be changed. We may not sell 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 is not soliciting an

offer to buy these securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION DATED AUGUST 30, 2017

Preliminary Prospectus

NextDecade Corporation

142,279,057 Shares of Common Stock

The selling stockholders named in this prospectus (the “Selling Stockholders”) may offer and sell from time to time up to 142,279,057 shares of our

Common Stock, covered by this prospectus, which includes: (i) 103,123,858 shares of our Common Stock issued to the Selling Stockholders, (ii) up

to 12,081,895 shares of our Common Stock that are issuable upon the exercise of Warrants issued in connection with our initial public offering,

which closed on March 23, 2015, and that are exercisable for one share of Common Stock at an exercise price of $11.50 per share (the “Warrants”),

(iii) up to 19,573,304 shares of our Common Stock that are issuable to certain of our Selling Stockholders upon the Company achieving certain

milestones (the “Contingent Shares”) and (iv) up to 7,500,000 restricted shares of Common Stock that are issuable to certain of our Selling

Stockholders upon the Company’s achieving certain milestones (the “Restricted Stock”).

We will not receive any proceeds from the sale of shares of Common Stock by the Selling Stockholders or by us pursuant to this prospectus, except

with respect to amounts received by us upon the exercise of the Warrants. However, we will pay the expenses, other than any underwriting discounts

and commissions, associated with the sale of shares pursuant to this prospectus.

Our registration of the securities covered by this prospectus does not mean that the Selling Stockholders will offer or sell any of the shares. The

Selling Stockholders may sell the shares of Common Stock covered by this prospectus in a number of different ways and at varying prices, in each

case subject to the Sale Restriction (as defined herein), as applicable. For more information, please read “Summary—Sale Restriction.” We provide

more information about how the Selling Stockholders may sell the shares in the section entitled “Plan of Distribution.”

On July 24, 2017 (the “Closing Date”), pursuant to the terms and subject to the conditions set forth in the Agreement and Plan of Merger, dated April

17, 2017 (the “Merger Agreement”), entities affiliated with certain members of NextDecade, LLC (“NextDecade, LLC”) (the “Blocker Companies”)

merged with and into Harmony Merger Corp. (“Harmony”) (each a “Blocker Merger” and, together, the “Blocker Mergers”), with Harmony being

the surviving entity of the Blocker Mergers and, immediately thereafter Harmony Merger Sub, LLC (“Merger Sub”) merged with and into

NextDecade, LLC (the “Merger” and together with the Blocker Mergers, the “Transactions”) with NextDecade, LLC being the surviving entity of the

Merger and becoming a wholly-owned subsidiary of Harmony (the “Business Combination”).

We filed a Definitive Proxy Statement on Schedule 14A with the SEC, dated June 29, 2017, in respect of a special meeting of stockholders, at which

our stockholders voted to approve the Business Combination, the Merger Agreement and certain other related matters. Upon the consummation of the

Business Combination, we changed our corporate name to “NextDecade Corporation.” For more information on the Business Combination and

NextDecade Corporation, please read our Definitive Proxy Statement on Schedule 14A, filed with the SEC on June 29, 2017.

Our Common Stock is traded on Nasdaq under the symbol “NEXT” and the Warrants trade under the symbol “NEXTW.” On August 29, 2017, the

last reported sales price of the Common Stock was $9.84 per share and of the Warrants was $0.87 per warrant.

We are an “emerging growth company,” as that term is defined under the federal securities laws and, as such, are subject to certain reduced public

company reporting requirements.

Please read “Risk Factors” on page 6 to read about factors you should consider before investing in our securities.

This prospectus may not be used to offer and sell any securities unless accompanied by a prospectus supplement.

Neither the Securities and Exchange Commission (“SEC”) nor any state securities commission nor any other regulatory body has approved

or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus. Any representation to the contrary is a

criminal offense.

The date of this prospectus is

, 2017.

Form S-3 - Registration Statement Under The Securities Act Of 1933 - United States Securities And Exchange Commission Page 4