The flight crew of any airliner needs to talk to ground control or to air traffic control officers before, during, and after a flight. This tends to reduce the risks of their aeroplane bumping into other aeroplanes. A standard company call-sign will normally be spoken before the flight number by both the aircrew and the relevant flight controllers.

Most of these call-signs relate very closely to the airline's trade name. The digits making up the flight number are shown in published timetables of the airline and also on the arrivals and departures screens that are found at most airports (and on their websites). It is clearly important that the verbal instructions passed by air traffic control officers are heard and responded to in the specific aircraft that they are directing to turn/climb/decelerate, etc. For that reason, company call-signs are internationally regulated and agreed to be sufficiently distinctive. This helps to minimise the chances of misunderstandings, and thus the risks of aeroplanes leaving their authorised course.

This is a list of the less obvious call-signs in use by many airlines, in alphabetic order of airline name. A few air forces are included too:

Some of the operators listed may have ceased trading or merged or updated their names. The country stated is the one in which the majority of their aircraft are believed to be registered, it may not always be the country in which the operator is legally incorporated. Airlines whose names are self-evident from the similarity of their call-signs are generally omitted from this list.