Medicare is a federal health insurance program in the United States that provides coverage for certain groups of individuals. It was established in 1965 under the Social Security Administration and is primarily aimed at older Americans aged 65 and above. However, it also covers certain individuals with disabilities and those with end-stage renal disease (ESRD) or amyotrophic lateral sclerosis (ALS).

Medicare consists of several parts, each covering different aspects of healthcare:

1. Medicare Part A (Hospital Insurance): Part A covers inpatient hospital care, skilled nursing facility care, hospice care, and some home health services. Most people do not have to pay a premium for Part A if they or their spouse have paid Medicare taxes while working.

2. Medicare Part B (Medical Insurance): Part B covers outpatient services, doctor visits, preventive care, durable medical equipment, laboratory tests, and some medically necessary services. Part B requires a monthly premium, which is determined based on income.

3. Medicare Part C (Medicare Advantage): Part C allows private insurance companies to offer Medicare-approved plans as an alternative to original Medicare (Parts A and B). These plans often include additional benefits such as prescription drug coverage (Part D), vision, dental, and hearing services. Medicare Advantage plans must provide at least the same level of coverage as original Medicare.

4. Medicare Part D (Prescription Drug Coverage): Part D is optional and provides prescription drug coverage. It helps beneficiaries pay for the cost of prescription medications. Part D plans are offered by private insurance companies approved by Medicare.

It's important to note that while Medicare covers a significant portion of healthcare costs, it does not cover all expenses. Beneficiaries are responsible for certain out-of-pocket costs, including deductibles, copayments, and coinsurance.

To enroll in Medicare, individuals generally become eligible at age 65 or when they meet specific disability requirements. The enrollment process is handled through the Social Security Administration or the Railroad Retirement Board.

Medicare plays a vital role in ensuring access to healthcare for millions of Americans, providing a safety net of coverage for medical services, treatments, and medications.