This from Physicians for a National Health Program: 
A single-payer national health insurance is a system in which a single public or quasi-public agency organizes health financing, but delivery of care remains largely private.
Currently, the U.S. health care system is outrageously expensive, yet inadequate. Despite spending more than twice as much as the rest of the industrialized nations ($7,129 per capita), the United States performs poorly in comparison on major health indicators such as life expectancy, infant mortality and immunization rates.
Moreover, the other advanced nations provide comprehensive coverage to their entire populations, while the U.S. leaves 45.7 million completely uninsured and millions more inadequately covered.
The reason we spend more and get less than the rest of the world is because we have a patchwork system of for-profit payers. Private insurers necessarily waste health dollars on things that have nothing to do with care: overhead, underwriting, billing, sales and marketing departments as well as huge profits and exorbitant executive pay. Doctors and hospitals must maintain costly administrative staffs to deal with the bureaucracy. Combined, this needless administration consumes one-third (31 percent) of Americans’ health dollars.
Single-payer financing is the only way to recapture this wasted money. The potential savings on paperwork, more than $350 billion per year, are enough to provide comprehensive coverage to everyone without paying any more than we already do.
Under a single-payer system, all Americans would be covered for all medically necessary services, including: doctor, hospital, preventive, long-term care, mental health, reproductive health care, dental, vision, prescription drug and medical supply costs. Patients would regain free choice of doctor and hospital, and doctors would regain autonomy over patient care.
Physicians would be paid fee-for-service according to a negotiated formulary or receive salary from a hospital or nonprofit HMO / group practice. Hospitals would receive a global budget for operating expenses. Health facilities and expensive equipment purchases would be managed by regional health planning boards.
A single-payer system would be financed by eliminating private insurers and recapturing their administrative waste. Modest new taxes would replace premiums and out-of-pocket payments currently paid by individuals and business. Costs would be controlled through negotiated fees, global budgeting and bulk purchasing.