Doctors often treat similar patients differently, affecting health and spending. We review the recent literature on physician decision making through the lens of a model that incorporates doctors diagnostic and procedural skills, beliefs, and incentives as well as differences in patient pools. The quality of decision making is affected by training, experience, peer effects, financial incentives, and time constraints. Interventions to improve decision making include providing information, guidelines, and technologies like electronic medical records and algorithms. Economists have made progress in understanding doctor decision making, but our ability to apply that knowledge to improve health care is still limited.