UNITED STATES SECURITIES AND EXCHANGE COMMISSION ☒ 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 For the transition period from _______ to _______ Commission File Number 0-25837 HEIDRICK & STRUGGLES INTERNATIONAL, INC. (Exact Name of Registrant as Specified in its Charter) (State or Other Jurisdiction of Incorporation or Organiza ...