<p>Police co-responder programs are collaborations between law enforcement and healthcare institutions where behavioral health professionals are embedded within police departments to support officers responding to incidents involving mental health and/or substance use. Research suggests that co-responder programs, which have existed for over 20 years in the United States and have become particularly popular in recent years, have the potential to decrease police use of force and divert individuals experiencing behavioral health crises from the criminal justice system. However, scant knowledge exists about the role of behavioral health professionals in these programs. This qualitative study examines nearly three years of clinical notes from the Boston Police Department’s co-response program. Using an inductive approach incorporating aspects of grounded theory and thematic analysis, we analyzed notes from 4,111 co-response encounters between July 2019 and March 2022. Our study yielded a conceptual framework with three domains. First, behavioral health professionals interacted with a wide range of community members, including: police personnel; individuals experiencing behavioral health crises; family members of individuals in crisis; and healthcare and social services providers. Second, and through these interactions, behavioral health professionals assessed behavioral health symptoms, behavioral health history, and indicators of risk. Finally, and in response to their assessments, behavioral health professionals provided clinical supports, police assistance, and general assistance to multiple community members. Our findings suggest potential mechanisms by which co-response programs impact both police and behavioral health outcomes. Implications for practice, policy, and future research are discussed.</p>