Like any insurance program, there are detailed rules about who can participate in Medicare and limits to what medical costs Medicare will help pay for.

The federal government is in charge of Medicare. Some parts of Medicare are now run by private companies, but those companies have to follow rules laid out by Medicare.

“Medicare” is actually a collection of related programs. Each program will help pay for a different aspect of your medical care. The programs are called “parts” and are named by letters. In general:

• Medicare Part A helps pay for medical care you get while you’re in a hospital.
• Medicare Part B helps pay for medical care you get outside of a hospital, like when you go to the doctor’s office.
• Medicare Part C, also known as Medicare Advantage, is a way to get Part A, B, and sometimes Part D coverage through private companies.
• Medicare Part D helps pay for prescription drugs.

Each Medicare Part has different rules for how you sign up, how much it costs, which medical costs it helps with, and how much of the costs it will help pay for.