It depends. If you are already collecting your Social Security benefits when you turn 65, then you should automatically receive your Medicare card with both Medicare Part A and Medicare Part B already activated. However, if you have chosen to delay your Social Security benefits, and you want to enroll into Medicare, then you'll need to take action and apply for Medicare Part B. This can be done with a short form CMS 40B from CMS. Here's the Medicare Part B application https://www.cms.gov/Medicare/CMS-Forms/CMS-Forms/Downloads/CMS40B-E.pdf