UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, DC 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): February 16, 2012 February 16, 2012

MAXWELL TECHNOLOGIES, INC.

(Exact Name of Registrant as Specified in its Charter)

5271 Viewridge Court, Suite 100

San Diego, California 92123

(Addresses of principal executive offices, including zip code)

(858) 503-3300

(Registrant’s telephone number, including area code)

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):

Item 1.01 Entry into a Material Definitive Agreement.

On February 16, 2012, Maxwell Technologies, Inc. (“Maxwell” or “we”) entered into an At-the-Market Equity Offering Sales Agreement (“Sales Agreement”) with Citadel Securities LLC (“Citadel”) pursuant to which we may sell, at our option, up to an aggregate of $30.0 million in shares of our common stock through Citadel, as sales agent. Sales of the common stock made pursuant to the Sales Agreement, if any, will be made on the NASDAQ Capital Market under our previously filed and currently effective Registration Statement on Form S-3 (File No. 333-173311) by means of ordinary brokers’ transactions at market prices. Additionally, under the terms of the Sales Agreement, we may also sell shares of our common stock through Citadel, on the NASDAQ Capital Market or otherwise, at negotiated prices or at prices related to the prevailing market price. Under the terms of the Sales Agreement, we may also sell shares to Citadel as principal for Citadel’s own account at a price agreed upon at the time of sale pursuant to a separate terms agreement to be entered into with Citadel at such time. Citadel will use its commercially reasonable efforts to sell our common stock from time to time, based upon our instructions (including any price, time or size limits or other customary parameters or conditions we may impose). We cannot provide any assurances that we will issue any shares pursuant to the Sales Agreement. We will pay Citadel a commission equal to 2% of the gross proceeds from the sale of shares of our common stock under the Sales Agreement, if any. We have also agreed to reimburse Citadel for certain expenses incurred in connection with entering into the Sales Agreement and have provided Citadel with customary indemnification rights. The offering of common stock pursuant to the Sales Agreement will terminate upon the earlier of (a) the sale of all of the common stock subject to the Sales Agreement or (b) the termination of the Sales Agreement by us or Citadel. Either party may terminate the agreement in its sole discretion at any time upon written notice to the other party.

The Sales Agreement, which is filed as Exhibit 10.1 to this Current Report on Form 8-K, is incorporated herein by reference. The foregoing description of the Sales Agreement does not purport to be complete and is qualified in its entirety by reference to such exhibit. The representations and warranties contained in the Sales Agreement are not for the benefit of any party other than the parties to such agreement and are not intended as a document for investors or the public generally to obtain factual information about us.

On February 16, 2012 we filed a press release announcing our entry into the Sales Agreement. The press release making such announcement is attached to this filing as Exhibit 99.1.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits.

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.

Date: February 16, 2012