Historians of medicine have struggled for centuries to make the case for history in medical education. They have developed many arguments about the value of historical perspective, but their efforts have faced persistent obstacles, from limited resources to curricular time constraints and skepticism about whether history actually is essential for physicians. Recent proposals have suggested that history should ally itself with the other medical humanities and make the case that together they can foster medical professionalism. We articulate a different approach and make the case for history as an essential component of medical knowledge, reasoning, and practice. History offers essential insights about the causes of disease (e.g., the non-reductionistic mechanisms needed to account for changes in the burden of disease over time), the nature of efficacy (e.g., why doctors think that their treatments work, and how have their assessments changed over time), and the contingency of medical knowledge and practice amid the social, economic, and political contexts of medicine. These are all things that physicians must know in order to be effective diagnosticians and caregivers, just as they must learn anatomy or pathophysiology. The specific arguments we make can be fit, as needed, into the prevailing language of competencies in medical education.