In recent years, attempts to capture and leverage a firm’s knowledge resources have become a primary focus in the pursuit of competitive advantage. Business leaders increasingly look to their firms’ bases of knowledge as their most critical strategic resource. This trend has led to the adoption of knowledge management initiatives aimed at leveraging the knowledge of individuals to advance the economic interests of an organization. Within such an effort, knowledge sharing behavior is an essential precondition for success. This study explores the determinants of knowledge sharing by applying Ajzen’s Theory of Planned Behavior to the context of knowledge management. The model provides support for an emphasis on relationship issues in the development of knowledge management programs. In addition, the model addresses both formal and informal features of organizational contexts that can affect knowledge sharing behavior. The model contributes to the study of knowledge management by addressing elements of a firm’s formal policies that may promote or inadvertently discourage knowledge sharing and by providing a robust framework for the analysis of knowledge sharing.