"Universal Coverage" and the "Single-Payer System" are two
separate yet closely related concepts.
"Universal coverage" refers to a health care system where
every individual has health coverage.
According to the U.S. Census Bureau, there were 46.6 million Americans
without health insurance coverage in 2005.
In contrast, there are no uninsured Canadian citizens--their government-run system provides universal coverage.
A "single-payer system" is one in which there is one party--usually the government--responsible for paying health care claims.
This contrasts with the current U.S. health care system, where thousands of private insurance companies are responsible for paying some claims, while federal and state governments are responsible for others.
In most cases, "universal coverage" and "single-payer system" go hand-in-hand, because a country's federal government is the most likely candidate to administer and pay for a health care system covering millions of people.
It is hard to imagine a private entity having the resources--or even the inclination--to establish a nationwide health care coverage system.
However, it is possible to have universal coverage without having a single-payer system. For example, some experts have suggested that we incrementally reform the U.S. health care system to provide a government-funded safety net for the sick and poor, while requiring those more fortunate to purchase their own policies.
Various political interests will likely prevent this from ever happening, but it is possible to construct such a system, which would provide universal coverage with multiple payers.
While it is theoretically possible to have a single-payer system
without having universal coverage, it is
extremely unlikely to ever occur because the single-payer would undoubtedly be the federal government.
If our government adopts such a system, it would
not be politically viable for them to
exclude any citizen from coverage.