This book constitutes the proceedings of the First International Symposium, ToM for Teams 2021, held in Washington, DC, USA, during  November 4-6, 2021,  Each chapter in this section tackles a different aspect of AI representing the thoughts and beliefs of human agents. The work presented herein represents our collective efforts to better understand ToM, develop AI with ToM capabilities (ASI), and study how to integrate such systems into human teams.