We talk of code sharing when two or more airlines share a scheduled service. Each of the airlines involved offers the flight concerned under its own flight number, but it is operated by only one airlines. So there can be different flight numbers for a single flight.

One example from the DUS timetable

Air Berlin and Etihad Airways offer a nonstop flight to New York (JFK) from Düsseldorf on a code sharing basis. The Etihad flight number for this flight is EY 1190, the Air Berlin flight number is AB 7450. The flight, however, is operated by Air Berlin.

Your ticket shows the flight number of the airline that issued it. On the information boards in the terminal, in the app and on the websites, all flight numbers associated with the flight are shown on a rolling basis with the notation “Code Sharing”.

Airline Alliances

The code sharing method is mainly used within airline alliances like Star Alliance, One World or Skyteam. This allows the airlines to offer flights that they do not operate themselves, but are operated by a partner airline of the alliance concerned.