Introduction: A practice embarks on a radical reformulation of how care is designed and delivered when it decides to integrate medical and behavioral health care for its patients and success depends on managing complex change in a complex system. We examined the ways change is managed when integrating behavioral health and medical care. Method: Observational cross-case comparative study of 19 primary care and community mental health practices. We collected mixed methods data through practice surveys, observation, and semistructured interviews. We analyzed data using a data-driven, emergent approach. Results: The change management strategies that leadership employed to manage the changes of integrating behavioral health and medical care included: (a) advocating for a mission and vision focused on integrated care; (b) fostering collaboration, with a focus on population care and a team-based approaches; (c) attending to learning, which includes viewing the change process as continuous, and creating a culture that promoted reflection and continual improvement; (d) using data to manage change, and (e) developing approaches to finance integration. Discussion: This paper reports the change management strategies employed by practice leaders making changes to integrate care, as observed by independent investigators. We offer an empirically based set of actionable recommendations that are relevant to a range of leaders (policymakers, medical directors) and practice members who wish to effectively manage the complex changes associated with integrated primary care.