The Medicare Annual Enrollment Period (AEP), also known as Open Enrollment, is the annual fall window from October 15 to December 7 when Medicare beneficiaries can review their current plans and make changes to their Medicare Advantage (Part C) or Part D (prescription drug) coverage. During this time, individuals can switch between Medicare Advantage plans, return to Original Medicare, enroll in a Part D plan, or change Part D plans, with new coverage taking effect on January 1 of the following year.