Airline alliances are partnerships between a group of airlines. There are three main benefits for the consumer:
1) You earn miles when you travel with any airline in your airline alliance 2) You get status benefits on all partner airlines 3) Airlines within the same network use codesharing
Codesharing means that airlines share flights. You purchase a seat with one airline but the flight is operated by another airline. This allows for greater access through the airline's network and prevents you from having to book separate flights. As a result, your trip will be cheaper and your luggage will be checked through to your final destination.
There are three airline alliances: Star Alliance, One World and Skyteam. See below for details of each network.
The largest of the three airline alliances is Star Alliance with 27 members, followed by Sky Team with 15 and One World with 12 members. See below for an overview of the three alliances.