MMSI stands for Maritime Mobile Service Identity. This is a unique 9-digit number assigned to boats with certain kinds of radio equipment. You can think of it as a Social Security number for your boat. Search and rescue authorities including the Coast Guard use the MMSI to learn background information about a vessel in distress (e.g., owner’s name, intended route, and other radio equipment on board). An accurate MMSI database helps to protect lives and property by reducing the time needed to locate vessels in distress. The MMSI number also has non-emergency functions. When properly set up in your Marine VHF radio, it allows you to see the name of who is calling (like caller ID), set a notification so you can see if you missed a call, or alert a buddy that you want to speak with them without having to listen to every unrelated call on Channel 16.