The IATA airport code is a set of three letters assigned to each airport around the world. These codes are designated by the International Air Transport Association, or IATA. The codes are not unique: 300 of around 20,000 total codes are used by more than one airport. A common example of their use is the letters shown clearly on the luggage tags which ticket agents slap on the bags at check-in time.
It is the full list of IATA codes for all Spanish airports:
Find further information inside IATA official website: www.iata.org.