Shared decision making, a collaborative approach between patient and provider that considers the patient's values and preferences in addition to the scientific evidence, is a complex clinical activity that has not realized its full potential. Gaps in education and training have been cited as barriers to shared decision making, and evidence is inconsistent on effective educational interventions. Because individual agents with their own social and behavioral contexts co-construct a shared decision, the educational approach may need to consider the role of patient agency and sociocultural influences. To address the inherent complexity in shared decision making, the authors identified cultural historical activity theory (CHAT) as a framework for analysis. Although certainly not the only relevant theory, CHAT offers an appropriate lens through which the multivoiced nature of shared decision making can be more clearly appreciated. In this article, the authors demonstrate the application of CHAT as a lens for researchers and educators to examine the complexity of shared decision making. The fictitious case presented in this article describes the use of CHAT with a patient who experiences 2 clinical encounters; during the second, shared decision making takes place. Elements of the case are threaded through the article, demonstrating a sample analysis of the interacting activity systems of the patient and physician and highlighting inherent tensions and contradictions. The authors propose CHAT as a tool for future research around the role of agency in shared decision making and other complex topics and as a framework for design of novel instructional strategies. Although not applicable to all topics and settings, CHAT has significant potential within health professions education.