Medicare is a federal health insurance program for persons 65 or older, persons of any age with permanent kidney failure, and certain disabled persons.

Medicare is administered by the Centers for Medicare & Medicaid Services (CMS), a federal agency in the Department of Health and Human Services. Social Security Administration offices across the country take applications for Medicare, collect premiums, and provide general information about the program. Various commercial insurance companies are under contract with CMS to process and pay Medicare claims, and groups of doctors and other health care professionals have contracts to monitor the quality of care delivered to Medicare beneficiaries. CMS also forms partnerships with the thousands of providers of health care services: hospitals, nursing homes, and home health agencies; doctors; suppliers of medical equipment; clinical laboratories; and managed care plans such as health maintenance organizations (HMOs). 

Medicare consists of Hospital Insurance (Part A), Medical Insurance (Part B), Medicare Advantage (Part C) (formerly known as Medicare+Choice), and Prescription Drug Insurance (Part D).