There are three enrollment periods for Medicare, which serve different purposes and have specific eligibility requirements and timeframes. Here are the three enrollment periods:

1. Initial Enrollment Period (IEP): This is the first opportunity to enroll in Medicare and generally occurs around your 65th birthday. It lasts for a total of seven months, starting three months before your birth month and ending three months after.

2. General Enrollment Period (GEP): If you missed your Initial Enrollment Period, you can sign up during the General Enrollment Period, which runs from January 1 to March 31 each year. However, late enrollment penalties may apply.

3. Special Enrollment Period (SEP): This period allows you to enroll in or make changes to your Medicare coverage outside of the standard enrollment periods. Qualifying events, such as moving to a new location or losing other health coverage, can trigger a Special Enrollment Period.

Its important to note that there is also an Annual Enrollment Period (AEP), which runs from October 15 to December 7 each year. During this time, anyone can make changes to their coverage and enroll in a Medicare plan. However, this is not considered one of the three enrollment periods for Medicare.