Medicare is the United States federal health insurance program for people aged 65 and older, as well as certain younger individuals with disabilities and those with end-stage renal disease. Established in 1965 under the Social Security Act, it is administered by the Centers for Medicare & Medicaid Services (CMS), a division of the U.S. Department of Health and Human Services.
The program is organized into four parts: Part A (hospital insurance), Part B (medical insurance), Part C (Medicare Advantage, offered through private insurers), and Part D (outpatient prescription drug coverage). It is financed through a combination of payroll taxes, beneficiary premiums, and general federal revenues. Medicare plays a central role in U.S. healthcare policy and spending, including coverage and reimbursement for medical services and prescription medicines, shaping access, utilization, and market dynamics across the healthcare sector.