A flight information service (FIS) is a form of air traffic service which is available to any aircraft within a flight information region (FIR), as agreed internationally by ICAO.
It is defined as information pertinent to the safe and efficient conduct of flight, and includes information on other potentially conflicting traffic, possibly derived from radar, but stopping short of providing positive separation from that traffic.
In aviation, a flight information region (FIR) is a specified region of airspace in which a flight information service, an alerting service (ALRS), and an area control centre are provided. The International Civil Aviation Organization (ICAO) delegates which country is responsible for the operational control of a given FIR. FIRs are the largest regular division of airspace in use in the world today, and have existed at least since 1947.
Smaller countries' airspace is encompassed by a single FIR; larger countries' airspace is subdivided into a number of regional FIRs.