The Patient Protection and Affordable Care Act (ACA) of 2010 is landmark legislation designed to expand access to health care for virtually all legal U.S. residents. A vital but controversial provision of the ACA requires individuals to maintain health insurance coverage or face a tax penalty—the individual mandate. We examine the constitutionality of the individual mandate by analyzing relevant court decisions. A critical issue has been defining the “activities” Congress is authorized to regulate. Some judges determined that the mandate was constitutional because the decision to go without health insurance, that is, to self-insure, is an activity with substantial economic effects within the overall scheme of the ACA. Opponents suggest that Congress overstepped its authority by regulating “inactivity,” that is, compelling people to purchase insurance when they otherwise would not. The U.S. Supreme Court is set to review the issues and the final ruling will shape the effectiveness of health reform.