The ICAO airport code or location indicator is a four-letter alphanumeric code designating each airport around the world. These codes are defined by the International Civil Aviation Organization, and published in ICAO Document 7910: Location Indicators.

The ICAO codes are used by air traffic control and airline operations such as flight planning. They are not the same as the IATA codes encountered by the general public, which are used for airline timetables, reservations, and baggage handling. For example, travellers who use London's Heathrow Airport will most likely be familiar with its IATA code: LHR. The travelling public are less likely, however, to be familiar with the ICAO code: EGLL.

ICAO codes are also used to identify other locations such as weather stations, International Flight Service Stations or Area Control Centers, whether or not they are located at airports.