Automatic Identification System (AIS) is intended primarily for enhancing the safety of ships at sea by reducing the chance of collisions. AIS allows ships to view marine traffic in their local area and to be seen by that traffic; data is normally overlaid on a radar, electronic chart display system and other devices. AIS is also used by vessel traffic services (VTS), maritime surveillance systems and logistic tracking services.

AIS is particularly useful to identify commercial vessels as the data transmitted includes the vessel name, MMSI number, heading, speed as well as other information to identify the purpose and destination of that vessel. AIS is based on VHF communication, so is normally effective to distances of 20 – 200nm depending on antenna height and local atmospheric conditions.

The International Maritime Organization's International Convention for the Safety of Life at Sea requires AIS to be fitted aboard international voyaging ships with gross tonnage (GT) of 300 or more tons, and all passenger ships regardless of size. It is estimated that more than 40,000 ships currently carry AIS class A and many smaller vessels (fishing vessels, working vessels and leisure craft) may also carry Class A or Class B transponders voluntarily to enhance their navigational operations. Some countries impose regulations for other vessels to require them to carry AIS, including fishing, leisure and other powered craft.