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):

May 24, 2017

COLUMBIA BANKING SYSTEM, INC.

(Exact name of registrant as specified in its charter)

Washington

(State or other jurisdiction of incorporation)

1301 A Street

Tacoma, WA 98402

(Address of principal executive offices) (zip code)

Registrant’s telephone number, including area code: (253) 305-1900

(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):

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) of Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

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 13(a) of the Exchange Act. ☐

On May 24, 2017, Columbia Banking System, Inc. (the “Company”) held its 2017 Annual Meeting of Shareholders (the “2017 Annual Meeting”). There were 58,325,968 shares outstanding and entitled to vote at the 2017 Annual Meeting; of those shares, 54,707,247 were present in person or by proxy. The following matters were voted upon at the 2017 Annual Meeting:

The following is a summary of the voting results for the matters voted upon by the shareholders.

1. Election of Directors

2. Advisory (non-binding) Approval of Executive Compensation

3. Advisory (non-binding) Approval of Frequency of Future Advisory Votes on Executive Compensation

4. Advisory (non-binding) Appointment of Independent Registered Public Accounting Firm

Based on the Board of Directors’ recommendation in the proxy statement for the 2017 Annual Meeting and the voting results with respect to the advisory vote on the frequency of future advisory votes on executive compensation, the Company has determined to hold an advisory vote on executive compensation annually.

On May 25, 2017, the Company issued a press release announcing that Columbia State Bank (the “Bank”), a wholly-owned subsidiary of the Company, has entered into an agreement with the Federal Deposit Insurance Corporation (the “FDIC”), dated as of May 23, 2017, to terminate all existing loss share agreements by and between the Bank and the FDIC. A copy of the press release is attached hereto as Exhibit 99.1 and is incorporated herein by reference.

The following exhibits are being filed herewith:

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.

EXHIBIT INDEX