UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

DATE OF REPORT (DATE OF EARLIEST EVENT REPORTED): March 17, 2017

PULMATRIX, INC.

(Exact name of registrant as specified in its charter)

99 Hayden Avenue, Suite 390

Lexington, MA 02421

(Address of principal executive offices) (Zip Code)

Registrant’s telephone number, including area code: (781) 357-2333

Not Applicable

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

On March 17, 2017, Pulmatrix, Inc. (the “Company”) entered into an At-The-Market Sales Agreement (the “Sales Agreement”) with BTIG, LLC (“BTIG”) to act as the Company’s sales agent with respect to the issuance and sale of up to $11,000,000 of the Company’s shares of common stock, par value $0.0001 per share (the “Shares”), from time to time in an at-the-market public offering (the “Offering”).

Sales of the Shares, if any, through BTIG, will be made directly on the NASDAQ Global Market, on any other existing trading market for the Shares, to or through a market maker or through an electronic communications network, or by any other method permitted by law. In addition, if expressly authorized by the Company, BTIG may also sell the Shares in privately negotiated transactions.

Under certain circumstances, the Company or BTIG may suspend the sale of the Shares under the Sales Agreement or terminate the Sales Agreement. The Sales Agreement will automatically terminate when the sale of Common Shares reaches an aggregate offering amount equal to $11,000,000, or sooner if terminated as permitted therein.

The Company will pay BTIG a commission equal to 3.0% of the gross proceeds from the sale of the Shares pursuant to the Sales Agreement.

The Sales Agreement contains representations, warranties and covenants that are customary for transactions of this type. In addition, the Company has agreed to indemnify BTIG against certain liabilities, including liabilities under the Securities Act of 1933, as amended. A copy of the Sales Agreement is filed as Exhibit 1.1 to this Current Report on Form 8-K and is incorporated herein by reference. The description of the Sales Agreement is qualified in its entirety by reference to Exhibit 1.1 to this Current Report on Form 8-K.

The Shares will be sold and issued pursuant the Company’s shelf registration statement on Form S-3 (File No. 333-212546), which was previously declared effective by the Securities and Exchange Commission, and a related prospectus.

In connection with the Offering, the legal opinion of Haynes and Boone, LLP as to the legality of the Shares is being filed as Exhibit 5.1 to this Current Report on Form 8-K.

This Current Report on Form 8-K, including the exhibits filed herewith, is not an offer to sell or the solicitation of an offer to buy the Shares or any other securities of the Company, nor shall there by any offer, solicitation or sale of the Shares or any other securities of the Company in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of such state.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.