Purpose: The purpose of the study was to understand better the clinical collaboration process among primary care physicians (PCPs), case managers (CMs), and geriatricians in integrated models of care. Methods: We conducted a qualitative study with semistructured interviews. A purposive sample of 35 PCPs, 7 CMs, and 4 geriatricians was selected in 2 integrated models of care for frail elderly patients in Canada and France: System of Integrated Care for Older Patients of Montreal and Coordination of Care for Older Patients of Paris. Data were analyzed using a grounded theory approach. Findings: The dynamics of the collaboration process develop in three phases: (1) initiating relationships, (2) developing real two-way collaboration, and (3) developing interdisciplinary teamwork. The findings suggest that CMs and geriatricians collaborated well from the start and throughout the care management process. Real collaboration between the CMs and the PCPs occurred only later and was mostly fostered by the interventions of the geriatricians. PCPs and geriatricians collaborated only occasionally. Implications: The findings provide information about PCPs' commitment to the integrated models of care, the legitimization of the CM's role among PCPs, and the appropriate positioning of geriatricians in such models.