This Recommendation provides guidance to administrations for the assignment and conservation of identity resources for the maritime mobile service. The limitations which constrain assignments for ships which utilize the satellite services of the global maritime distress and safety system (GMDSS) are described in this Recommendation. Annex 1 describes formats for maritime mobile service identities (MMSI) of ship stations@ coast stations@ aircraft participating in search and rescue operations and other safety-related communications@ automatic identification system (AIS) aids to navigation@ and craft associated with a parent ship. Annex 2 describes formats for identification of other maritime devices@ such as handheld VHF transceivers with digital selective calling (DSC) and global navigation satellite system (GNSS)@ AIS-search and rescue transmitter (AIS-SART)@ man overboard (MOB) and emergency position indicating radio beacon (EPIRB)-AIS. Annex 3 provides specific guidance to administrations for the assignment@ management and conservation of identity resources for the maritime mobile service. This guidance further instructs administrations on methods for the reuse of MMSI assignments@ particularly for the reuse of those with three trailing zeroes.