Evaluating implementation of complex interventions to improve care transitions and comparison across studies is challenging due to issues such as variation in methods and lack of reporting key evaluation elements. This article describes a framework for evaluating implementation of hospital to ambulatory care transitions interventions and application to a case study. We searched published and gray literature for relevant frameworks. We adapted the general Consolidated Framework for Implementation Research, adding elements relevant to other complex interventions. We refined these adaptations through structured expert input and application to case studies. Key adaptations included conceptualization around organizations, not just settings, and around patient- and caregiver-centeredness. Although these interventions are often oriented toward institutional outcomes such as readmissions, tailoring interventions to specific patient needs strengthens effectiveness. Coordination and communication are important between organizations and providers and with patients and caregivers. Roles of those involved in the intervention—providers, administrators, and facilitators from different organizations—are also key constructs. Finally, as these interventions often are tailored to specific settings and adapt over time, assessing intervention design—which components are implemented as part of the bundle, how they are actually implemented, and their differential impact on effectiveness—is critical.