Although leaders and other commentators have called for the medical profession's greater engagement in improving systems of care and population health, neither medical education nor the practice environment has fostered such engagement. Missing have been a clear definition of physicians' public roles, reasonable limits to what can be expected, and familiarity with tasks that are compatible with busy medical practices. We address these issues by proposing a definition and a conceptual model of public roles that require evidence of disease causation and are guided by the feasibility and efficacy of physician involvement. We then frame a public agenda for individual physicians and physician organizations that focuses on advocacy and community participation. By doing so, we aim to stimulate dialogue about the appropriateness of such roles and promote physician engagement with pressing health issues in the public arena.