Single payer means one entity, typically government, pays for care that may still be delivered privately. It is the most-discussed structural alternative to the current American system, and the debate concerns financing, provider payment, and transition as much as principle.
Single payer is not the same as government-run health care. In most single-payer systems hospitals and physicians remain independent; the change is in who pays and how prices are set. Medicare already operates on something close to this model for those over 65.
Financing would shift from premiums and out-of-pocket costs to taxes. Analyses generally agree total national health spending could fall through lower administrative costs and negotiated prices, while disagreeing on magnitude and on how much would move onto public budgets.
Provider payment is the crux. American hospitals and physicians are generally paid more than counterparts abroad, and rates set near current Medicare levels would represent a substantial reduction for many institutions, with disputed effects on access and rural hospital viability.