UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 10-Q (Mark One) For the transition period from to (IRS Employer Identification No.) Commission File Number 001-34091 MARKETAXESS HOLDINGS INC. (Exact name of registrant as specified in its charter) ☑ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2019 Delaware 52-2230784 (State or other jurisdiction of incorporation or organization) or ☐ TRANSITION RE ...

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 10-K (Mark One) ☑ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31, 2018 ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from to Commission File Number 001-34091 MARKETAXESS HOLDINGS INC. (Exact name of registrant as specified in its charter) 55 Hudson Yards, New York, New York 10001 (Addres ...