Medicare is a government national health insurance program in the United States, begun in 1965 under the Social Security Administration (SSA) and now administered by the Centers for Medicare and Medicaid Services (CMS). It primarily provides health insurance for Americans aged 65 and older, but also for some younger people with disability status as determined by the SSA, including people with end stage renal disease and amyotrophic lateral sclerosis (ALS or Lou Gehrig's disease).
In 2022, according to the 2023 Medicare Trustees Report, Medicare provided health insurance for 65.0 million individuals—more than 57 million people aged 65 and older and about 8 million younger people. According to annual Medicare Trustees reports and research by Congress' MedPAC group, Medicare covers about half of healthcare expenses of those enrolled. Enrollees almost always cover most of the remaining costs by taking additional private insurance and/or by joining a public Medicare Part C and/or Medicare Part D health plan.