There are four parts to Medicare: Medicare Part A, Hospital Insurance; Medicare Part B, Medical Insurance; Medicare Part C (Medicare Advantage), which was formerly known as "Medicare + Choice" and the new Medicare Part D, prescription drug coverage. Generally, people who are over age 65 and getting Social Security automatically qualify for Medicare Parts A and B. So do people who have been getting disability benefits for two years, people who have amyotrophic lateral sclerosis (Lou Gehrig's disease) and receive disability benefits, and people who have permanent kidney failure and receive maintenance dialysis or a kidney transplant.

Part A is paid for by a portion of Social Security tax. It helps pay for inpatient hospital care, skilled nursing care, hospice care and other services.

Part B is paid for by the monthly premiums of people enrolled and by general funds from the U.S. Treasury. It helps pay for doctors' fees, outpatient hospital visits, and other medical services and supplies that are not covered by Part A.

Part C (Medicare Advantage) plans allow you to choose to receive all of your health care services through a provider organization. These plans may help lower your costs of receiving medical services, or you may get extra benefits for an additional monthly fee. You must have both Parts A and B to enroll in Part C.

Part D (prescription drug coverage) is voluntary and the costs are paid for by the monthly premiums of enrollees and Medicare. Unlike Part B in which you are automatically enrolled and must opt out if you do not want it, with Part D you have to opt in by filling out a form and enrolling in an approved plan.

More information may be found in the Social Security Administration’s publication called Medicare, publication number 05-10043. Many of the Social Security Administration’s other publications are available on the Internet.

More information about all four parts of Medicare can be found at the Centers for Medicare and Medicaid Services website.