Exhibit 5.1

Troutman Pepper Hamilton Sanders LLP 3000 Two Logan Square, Eighteenth and Arch Streets Philadelphia, PA 19103-2799   troutman.com

February 12, 2021

Board of Directors

Windtree Therapeutics, Inc.

2600 Kelly Road, Suite 100

Warrington, Pennsylvania

Ladies and Gentlemen:

We are acting as counsel to Windtree Therapeutics, Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing of its registration statement on Form S-8 (the “Registration Statement”), filed with the Securities and Exchange Commission under the Securities Act of 1933, as amended (the “Act”), relating to the registration of an aggregate 311,000 shares of common stock, par value $0.001 per share, of the Company (the “Shares”), which may be issued pursuant to the exercise of non-qualified stock option awards granted to certain employees as inducements material to the individuals party thereto entering into employment with the Company (the “Inducement Awards”). This opinion letter is furnished to you at your request to enable you to fulfill the requirements of Item 601(b)(5) of Regulation S-K, 17 C.F.R. § 229.601(b)(5), in connection with the Registration Statement, and no opinion is expressed herein as to any matter pertaining to the contents of the Registration Statement or related prospectus, other than as expressly stated herein with respect to the issuance of the Shares.

For purposes of this opinion letter, we have examined copies of such agreements, instruments and documents as we have deemed an appropriate basis on which to render the opinions hereinafter expressed. In our examination of the aforesaid documents, we have assumed the genuineness of all signatures, the legal capacity of all natural persons, the accuracy and completeness of all documents submitted to us, the authenticity of all original documents, and the conformity to authentic original documents of all documents submitted to us as copies (including telecopies). As to all matters of fact, we have relied on the representations and statements of fact made in the documents so reviewed, and we have not independently established the facts so relied on. This opinion letter is given, and all statements herein are made, in the context of the foregoing.

As such counsel, we have examined such matters of fact and questions of law as we have considered appropriate for purposes of this letter. With your consent, we have relied upon certificates and other assurances of officers of the Company and others as to factual matters without having independently verified such factual matters. We are opining herein as to the General Corporation Law of the State of Delaware (the “DGCL”), and we express no opinion with respect to any other laws.

Windtree Therapeutics, Inc. February 12, 2021
Page 2

This opinion letter is based as to matters of law solely on the Delaware General Corporation Law, as amended. We express no opinion herein as to any other statutes, rules or regulations.

Based upon, subject to and limited by the foregoing, we are of the opinion that following (i) effectiveness of the Registration Statement, (ii) issuance of the Shares pursuant to the terms set forth in the stock option award agreements for the Inducement Awards (the “Inducement Grant Agreements”), and (iii) receipt by the Company of the consideration for the Shares specified in the resolutions of the Board of Directors or a duly authorized committee thereof, and the Inducement Grant Agreements, the Shares will be validly issued, fully paid, and nonassessable.

This opinion letter has been prepared for use in connection with the Registration Statement. We assume no obligation to advise you of any changes in the foregoing subsequent to the effective date of the Registration Statement.

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement. In giving this consent, we do not thereby admit that we are an “expert” within the meaning of the Act.

Very truly yours,

/s/ Troutman Pepper Hamilton Sanders LLP          

Troutman Pepper Hamilton Sanders LLP