Code sharing is the somewhat sneaky practice airlines engage in to give the illusion they offer more flights than aircraft they launch into the air. A code-share flight involves an aircraft engaged in a scheduled route being assigned different flight codes by partnering airlines, who represent the flight as being one of theirs. The flight may therefore use an aircraft that belongs to an airline different to what the passenger had expected.

It can make sense for airlines to establish code-share partnerships, especially as an alternative to flying unprofitable routes. A trans-continental flight might be a code-share between a major airline and several smaller airlines, who do not have the capacity to service the route. For example, Olympic Airlines flies from Athens to Bahrain, then Gulf Air takes passengers onwards to Australia as a code-shared flight. Connecting flights from major hubs to minor airports can be more efficiently coordinated, reducing the waiting time for transit passengers. Malaysia Airlines can claim it flies to several cities in the United Kingdom, with its code-share with British Midland. On popular international routes some airlines from one country ally themselves with airlines from the other, doubling capacity and giving passengers twice as many flights to choose from. British Airways and Cathay Pacific do this between Britain and Hong Kong.

The biggest gripe about code sharing is that passengers may feel they have been misrepresented about what airline they were going to fly, particularly if they think the airline that actually flies the route is inferior or does not contribute mileage to the passenger's frequent flier account.

So, if you are flying Air France's eleven hour code-share flight with Southern China Airlines from Paris to Guangzhou, expect kung fu over art house as the genre of the inflight movie.