The prospect of single-payer “Medicare-for-all” reform evokes enthusiasm and concern. Proponents maintain that a single-payer system would be the simplest route to universal coverage; every US resident would qualify for comprehensive insurance under a public, tax-financed plan that would replace private insurers, Medicaid, and Medicare. Others are concerned that costs would escalate or that the government would limit and underfund care, particularly hospital care, which commands the largest share of health spending; innovation might lag; and government may infringe on medical decisions.