The International Civil Aviation Organization (ICAO), an arm of the United Nations that ensures aviation regulations jive across different countries and continents, assigns codes generally used by air traffic control and by airlines in crafting their flight plans.

Three-letter airline designators are officially assigned by the International Civil Aviation Organization (ICAO), a specialized agency of the United Nations. These codes, such as SWA for Southwest or AAL for American Airlines, are unique to each aircraft operating agency and are primarily used for technical and flight operational purposes, including air traffic control and flight planning. This system is distinct from the more consumer-facing two-character codes (like WN or AA) assigned by the International Air Transport Association (IATA), which are used for ticketing, schedules, and reservations. ICAO's three-letter system was introduced in 1982 to replace an older two-letter format because the increasing number of global airlines had exhausted all available two-letter combinations. All official ICAO designators and their corresponding telephony call signs (like "SOUTHWEST" or "AMERICAN") are maintained in the ICAO Document 8585.