SCHEDULE 14A INFORMATION

Proxy Statement Pursuant to Section 14(a)

of the Securities Exchange Act of 1934 (Amendment No.     )

Filed by the Registrant  ☒

Filed by a Party other than the Registrant  ☐

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☐	Preliminary Proxy Statement	☐	Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))
☐	Definitive Proxy Statement
☒	Definitive Additional Materials
☐	Soliciting Material Pursuant to §240.14a-11(c) or §240.14a-12

COLUMBIA BANKING SYSTEM, INC.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

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☐	Check box if any part of the fee is offset as provided by Exchange Act Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid previously. Identify the previous filing by registration statement number, or the Form or Schedule and the date of its filing.
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See the reverse side of this notice to obtain proxy materials and voting instructions. *** Exercise Your Right to Vote *** Important Notice Regarding the Availability of Proxy Materials for the Shareholder Meeting to Be Held on May 22, 2019. You are receiving this communication because you hold shares in the above named company. This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side). We encourage you to access and review all of the important information contained in the proxy materials before voting. Meeting Information Meeting Type: Annual Meeting For holders as of: March 25, 2019 Date: Time: May 22, 2019 Location: William W. Philip Hall University of Washington Tacoma 1918 Pacific Avenue Tacoma, Washington COLUMBIA BANKING SYSTEM,INC. Columbia Banking System, Inc c/o Broadridge PO Box 1342 Brentwood, NY 11717 1918 Pacific Avenue Tacoma, Washington

Please Choose One of the Following Voting Methods Vote In Person: Many shareholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. At the meeting, you will need to request a ballot to vote these shares. Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow available and follow the instructions. Vote By Mail: You can vote by mail by requesting a paper copy of the materials, which will include a proxy card. How To Vote Before You Vote How to Access the Proxy Materials Proxy Materials Available to VIEW or RECEIVE: How to View Online: Have the information that is printed in the box marked by the arrow (located on the following page) and visit: www.proxyvote.com. How to Request and Receive a PAPER or E-MAIL Copy: If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request: 1) BY INTERNET: www.proxyvote.com 2) BY TELEPHONE: 1-800-579-1639 3) BY E-MAIL*: sendmaterial@proxyvote.com * If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked by the arrow (located on the following page) in the subject line. 0000414633_2 R1.0.1.18 1. Notice & Proxy Statement 2. AR/10K Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before May 08, 2019 to facilitate timely delivery.

Voting items 0000414633_3 R1.0.1.18 The Board of Directors recommends you vote FOR the following: 1. Election of Directors Nominees 1a. Craig D. Eerkes 1b. Ford Elsaesser 1c. Mark A. Finkelstein 1d. Eric S. Forrest 1e. Thomas M. Hulbert 1f. Michelle M. Lantow 1g. Randal L. Lund 1h. S. Mae Fujita Numata 1i. Hadley S. Robbins 1j. Elizabeth W. Seaton 1k. Janine T. Terrano The Board of Directors recommends you vote FOR proposals 2, 3 and 4. 2. To approve the Amended 2018 Equity Incentive Plan. 3. To vote on an advisory (non-binding) resolution to approve the compensation of Columbia's named executive officers. 4. To vote on an advisory (non-binding) resolution to appoint Deloitte & Touche LLP as our independent registered public accounting firm for fiscal year ending December 31, 2019. NOTE: Such other business as may properly come before the meeting or any adjournment thereof.

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