Part C is the part of Medicare policy that allows private health insurance companies to provide Medicare benefits. These Medicare private health plans, such as HMOs and PPOs, are known as Medicare Advantage Plans. If you want, you can choose to get your Medicare coverage through a Medicare Advantage Plan instead of through Original Medicare.

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Medicare Advantage Plans must offer at least the same benefits as Original Medicare (those covered under Parts A and B) but can do so with different rules, costs, and coverage restrictions. You also typically get Part D as part of your Medicare Advantage benefits package. Many different kinds of Medicare Advantage Plans are available. You may pay a monthly premium for this coverage, in addition to your Part B premium.

Medicare Supplement Policies (Medigap) are health insurance policies that offer standardized benefits to work with Original Medicare and are sold by private insurance companies.  If you have a Medigap policy, Original Medicare first pays its share for your care, and then Medigap pays all or part of the remaining costs, including deductibles, coinsurance, and copayments. Medigaps may also cover some health care costs that Medicare doesn’t cover at all, like care received when travelling out of the country. Medigaps only work with Original Medicare, if you have a Medicare Advantage Plan you cannot buy a Medigap. 

A Special Needs Plan (SNP) is a Medicare Advantage Plan (private health plan) that exclusively serves at least one of the following groups:

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• People who live in a nursing home or Intermediate Care Facility for the Mentally Disabled (either specific nursing homes or those in a certain area) and people who live in the community but require an institutional level of care;

• People who have both Medicare and Medicaid (dual-eligibles);

• People who have a specific chronic, severe or disabling condition defined by the plan (such as diabetes or heart disease).

Medicare Part D (Outpatient Prescription Drug Insurance) is the part of Medicare that provides outpatient prescription drug coverage. Part D is provided only through private insurance companies that have contracts with the government—it is never provided directly by the government (like Original Medicare is).