Airport check-in is the process whereby an airline approves airplane passengers to board an airplane for a flight. Airlines typically use service counters found at airports for this process, and the check-in is normally handled by an airline itself or a handling agent working on behalf of an airline. Passengers usually hand over any baggage that they do not wish or are not allowed to carry in the aircraft's cabin and receive a boarding pass before they can proceed to board their aircraft.

Check-in is usually the first procedure for a passenger when arriving at an airport, as airline regulations require passengers to check in by certain times prior to the departure of a flight. This duration spans from 15 minutes to 2 hours depending on the destination and airline (with self check in, this can be expanded to 30 days, if checking in by online processes). During this process, the passenger often has the ability to ask for special accommodations such as seating preferences, inquire about flight or destination information, accumulate frequent flyer program miles, or pay for upgrades. The airline check-in's main function, however, is to accept luggage that is to go in the aircraft's cargo hold and issue boarding passes. The required time is sometimes written in the reservation, sometimes written somewhere in websites, and sometimes only referred as "passengers should allow sufficient time for check-in".

In-town check-in service is a service offered by some cities such as Abu Dhabi, Seoul, Hong Kong, Delhi, Kuala Lumpur–International, London, Stockholm, Vienna and Taipei, where passengers may check in luggage in designated places within the city but outside the airport. This reduces check-in time and queuing at the airport.