Medicare is a federal health insurance program for people aged 65 and older, younger people with disabilities, and people with end-stage renal disease. It has four parts: Part A covers hospital insurance; Part B covers medical insurance; Part C covers Medicare Advantage plans; and Part D covers prescription drug plans. For most people, enrollment in Parts A and B is automatic based on their Social Security enrollment. However, some people need to sign up during an initial seven-month enrollment period. ERS retirees in Texas are enrolled in supplemental plans like HealthSelect Medicare Advantage that provide additional benefits and lower costs.