You're eligible for Original Medicare (Parts A and B) if:
1.) You're at least 65 years old, or you're under 65 and qualify on the basis of a disability or other special situation.
2.) You're a U.S. citizen or a legal resident who has lived in the U.S. for at least 5 consecutive years.
The 4 Basic Parts of Medicare
Part A, Hospital Coverage, is generally offered at no additional cost to qualifying individuals who have at least forty calendar quarters, ten years, of employment history in which Social Security taxes were paid for in the United States. Those without sufficient work history may be subject to significant premiums.
Part B, Doctors and Outpatient services, is optional coverage that requires a premium to be paid monthly. The premium will be based on, up to, the previous two years of annual income. Part B is not full coverage. There is still a deductible to be met and other out of pocket expenses. Even considering the coverage is optional, a late enrollment penalty can be added if you do not enroll after turning 65 and are not covered by you or your spouse's Employer Group Health Insurance (EGHI).
Part C, or Medicare Advantage plan, is provided by private insurance companies. They administer the benefits and combine coverage for Part A, Part B, usually Part C, and varying degrees of added benefits all in ONE PLAN. Examples of different types of plans include HMO's, PPO's, PFFS's, and SNP's. You can choose to get your Medicare coverage through a Medicare Advantage plan instead of Original Medicare, but you cannot have both.
Part D, or Prescription Drug Plans (PDPs), is the part of Medicare that provides prescription drug coverage. Medicare Part D Plans are provided only through private insurance companies that have legal agreements with the government; it’s never provided directly from the government. You can get coverage through a stand-alone plan or through a Medicare Advantage plan. Although optional, there are situations where late enrollment penalties may be applied if proper coverage is not established.