Unlike many Western nations, the United States does not manage or actively regulate the number, type, or geographic distribution of its physician workforce. As a result, medical trainees choose how and where to work. As with most free markets, equitable distribution is at risk without well-informed, evidence-based policies and incentives capable of promoting equitable access to appropriate care. This study contributes to understanding of important policy options and incentives by identifying factors that influence medical student and resident choices about medical specialties and location of practice. Specifically, it identifies factors that are associated with choice of primary care specialties, particularly family medicine, and with caring for rural and underserved populations.