The operating carrier is the airline that operates a flight using its own aircraft or an aircraft that it has leased to support its flight activity. The operating carrier is responsible for the safe and efficient operation of the flight, including the takeoff, en-route, and landing phases. The operating carrier may also be responsible for providing customer service, such as check-in, baggage handling, cargo and in-flight services.

In the case of code-share flights, more than one carrier's designator code and flight number may apply. In this case, the operating carrier is the airline that is actually operating the flight using its own aircraft or a leased aircraft. The other carrier or carriers involved in the code-share agreement are referred to as marketing carriers, as they are marketing and selling the flight under their own designator code and flight number. The operating carrier and the marketing carrier may have different agreements and responsibilities with regard to the code-share flight.