Medicare is a national social insurance program administered by the federal government. Medicare provides access to health insurance for Americans aged 65 and older who have paid into it (i.e. paid income tax in the US). Medicare is also available to some younger people with disabilities and to individuals with end-stage renal disease.

There are four components to the Medicare program: Part A, covering hospital care, and Part B, covering most other medical care, were part of the original Medicare program created in 1965. Medicare Part C, known as Medicare Advantage, is an option that allows beneficiaries to purchase all-in-one coverage through commercial insurance companies. Part D, added in 2004, covers prescription drugs. Most Medicare recipients pay premiums and incur out-of-pocket expenses as deductibles and coinsurance. Low-income recipients may have their premiums and cost-sharing obligations for Medicare Part A and/or B covered by Medicaid; this population is known as dual eligibles.  Many recipients purchase supplemental coverage, known as Medigap.