No provision of the Patient Protection and Affordable Care Act (PPACA) has been more contentious than the so-called “individual mandate,” the constitutionality of which is now before several appellate courts. Critics claim that the mandate represents an unprecedented attempt by the federal government to compel individual action. Yet, states frequently employ similar mandates to protect the public's health. These public health mandates have also often aroused deep opposition. This essay situates PPACA's mandate, and the opposition to it, in that broader context. The article reviews the arguments that public health's population perspective provides in support of mandates, as well as the reasons why mandates often ignite intense legal and political opposition. Most importantly, by holding individuals accountable for population-based problems, mandates may undercut the public health arguments that justify them. The article concludes by arguing that public health policymakers need to know more about the unintended political and legal costs of mandates.