An international airport is an airport typically equipped with customs and immigration facilities to handle international flights to and from other countries. Such airports are usually larger, and often feature longer runways and facilities to accommodate the large aircraft commonly used for international or intercontinental travel. International airports often host domestic flights (flights which occur within the country) in addition to international flights. In many smaller countries most airports are international airports, so the concept of an "international airport" has little meaning. In certain countries however, there is a sub-category of limited international airports which handle international flights, but are limited to short-haul destinations (often due to geographical factors) or are mixed civilian/military airports.

Many airports with regularly scheduled international service have the word "International" in their official names, but others, including such major airports as London Heathrow Airport, Detroit Metropolitan Wayne County Airport, and George Bush Intercontinental Airport do not. Conversely, some airports which call themselves international airports, especially in smaller United States cities, in fact have no scheduled international airline passenger service but do have customs and immigration facilities serving charter, cargo and general aviation flights. At many of these airports customs and immigration services are only available with several hours advance notice. One example of such an airport is Gerald R. Ford International Airport in Grand Rapids, Michigan. A few, such as Gary/Chicago International Airport in Gary, Indiana, are in fact not international airports at all; they are not designated as airports of entry but aspire to become such in the future and added "international airport" to their names as a marketing tool.

Other airports which previously served international flights now serve primarily domestic flights (international traffic having been redirected to a newer, larger airport in the area), but retain the "international" designation in their name. Examples of these are:

• Don Mueang International Airport (Old Bangkok Int'l), in Bangkok, Thailand, relieved by Suvarnabhumi Airport
• Tokyo International Airport (Haneda), in Tokyo, Japan, relieved by Narita International Airport (although Japan Airlines drops some routes between Haneda and Seoul, Shanghai and Hong Kong)
• Begumpet Airport in Hyderabad, India.
• Taipei Songshan Airport in Taipei, Taiwan (which retains its name as "Taipei International Airport" in Chinese), relieved by Taoyuan International Airport.
• Gimpo International Airport in Seoul, South Korea, relieved by Incheon International Airport
• Shanghai Hongqiao International Airport in Shanghai, People's Republic of China, relieved by Pudong International Airport.
• Halim Perdanakusuma International Airport in Jakarta, Indonesia, relieved by Soekarno-Hatta International Airport.

Many international airports also serve as "hubs", or places where non-direct flights may land and passengers switch planes. International airports often have many airlines represented, and many of these are often foreign.

Passengers connecting to domestic flights from an international flight generally must take their checked luggage through customs and re-check their luggage at the domestic airline counter, requiring extra time in the process. In some cases in Europe luggage can be transferred to the final destination even if it is a domestic connection.

In some cases, travelers and the aircraft can clear customs and immigration at the departure airport. As one example of this, are airports in Canada with United States border preclearance facilities. This allows flights from those airports to fly into US airports that do not have customs and immigration facilities. Luggage from such flights can also be transferred to a final destination in the U.S. through the airport of entry.