IATA vs ICAO codes

Two coding systems, two audiences: one prints on your bag tag, the other lives in the flight plan.

IATA codes — three letters

Assigned by the International Air Transport Association, IATA codes are the ones passengers see: on tickets, baggage tags, departure boards and airline apps. LHR is Heathrow, JFK is Kennedy. They are unique worldwide and are reassigned only when an airport closes or a code is retired.

ICAO codes — four letters

Assigned by the International Civil Aviation Organization and used in flight plans, air traffic control and weather reports. The first letter or two indicate the region or country — K for the contiguous United States, EG for the United Kingdom, RJ for Japan — and the rest identify the airfield. So Heathrow is EGLL and Kennedy is KJFK.

Where the systems overlap

Most large airports have both codes, but small airfields, heliports, seaplane bases and private strips often have only an ICAO or local identifier. Conversely, some codes look similar: a three-letter IATA code and a four-letter ICAO code for the same city share no digits, so mixing them up is a common travel-agency error.

Reading a code you find here

Every airport page lists the IATA code, the ICAO code, the local identifier, coordinates, elevation and runways, so you can confirm which system you are looking at before booking or filing.