The recent challenges to the Affordable Care Act (ACA), which has increased the number of individuals with health insurance in the United States but has had little effect on cost, has revived the debate about a single-payer health care system.¹ Whether a single-payer system is the answer or not depends on what question is being asked and what form single payer will take. Single payer can take many forms, and many questions can be asked. This Viewpoint considers 3 problems of US health care: the uninsured, poor health outcomes (relative to other high-income countries), and high cost. In discussing cost, it will be critical to consider the form that a single-payer health care system might take.