UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q ☑ Quarterly Report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 For the quarterly period ended June 30, 2021 OR ☐ Transition report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 Commission file number 001-34095 FIRST BUSINESS FINANCIAL SERVICES, INC. (Exact name of registrant as specified in its charter) Wisconsin 39-1576570 (State or other jurisdiction of incorporation or org ...