Maritime communication comprises communication between vessels and coast-stations, intraship communication and intership communication (internal communication when the vessel is berthing, casting off, leaving berth, loading and discharging).

An Urgency message indicates that there is serious danger for vessel, crew and passengers.

GMDSS will enable a vessel to communicate with coastal stations and other vessels at any time and under any circumstance.

Any message concerning maritime communications consists of three parts: the announcement of the message (which may be followed by the acknowledgement from the receiving station or vessel); the actual message and the ending of the message ("out").

The procedure used when announcing a message is called “Address and Identify”. The transmitting party addresses the receiving station(s) or vessel(s), after which he identifies his vessel.