An international flight is a form of commercial flight within civil aviation where the departure and the arrival take place in different countries. An important difference between international and domestic flights is that, before boarding the aircraft, passengers must undergo migration formalities and, when arriving to the destination airport, they must undergo both immigration and customs formalities, unless both the departure and arrival countries are members of the same free travel area, such as the Schengen Area. Airports serving international flights are known as international airports.