One of the often-discussed proposals to reform the health care system is a single-payer plan, sometimes called “Medicare for All.” Arguments for and against are wide ranging. There is also considerable confusion as to what “single payer” means and how it might operate. Consequently, this brief presents both a general picture of the most frequently mentioned single-payer proposal, and we delineate the advantages and disadvantages of the approach without taking a position on its advisability. Such clarification is necessary to advance a constructive debate over next steps for improving the US health insurance system. The authors first make five contextual points that are critical to better understanding the debate around single-payer plans, as well as a list of pros and cons.