A federal program that pays for certain health care expenses for people ages 65 or older, younger people with disabilities, and people with End Stage Renal Disease. People under 65 and disabled must be receiving disability benefits from either Social Security or the Railroad Retirement Board for at least 24 months. Enrollment in Medicare is automatic at age 65 for U.S. citizens and legal residents of the United States who have paid Medicare payroll taxes for a minimum of 10 years while employed or who have met other specific guidelines.