Airlines have increasingly been grouping up into three global alliances: Star Alliance, OneWorld, and SkyTeam. These alliances allow airlines to share their route networks, award redemptions, and partial elite status recognition. For example, United is a Star Alliance member so you can redeem United miles for an award flight on any partner airline worldwide, which makes those miles way more valuable! Alliances are also good for earning power–you can earn United miles on most Star Alliance partner flights.
Here are the alliances and a full list of their member airlines: (in alphabetical order):
Star Alliance: Adria Airways, Aegean Airlines, Air Canada, Air China, Air New Zealand, ANA, Asiana Airlines, Austrian, AviancaTACA Airlines, Blue1, Brussels Airlines, Copa Airlines, Croatia Airlines, EGYPTAIR, Ethiopian Airlines, LOT Polish Airlines, Lufthansa, Scandinavian Airlines, Singapore Airlines, South African Airways, SWISS, TAM Airlines, TAP Portugal, THAI, Turkish Airlines, United, US Airways
OneWorld: airberlin, American Airlines, British Airways, Cathay Pacific, Finnair, Iberia, Japan Airlines, LAN, Mexicana, Qantas, Royal Jordanian, and S7 Airlines.
SkyTeam: Aeroflot, Aerolineas Argentinas, Aeromexico, Air Europa, Air France, Alitalia, China Airlines, China Eastern, China Southern, Czech Airlines, Delta Air Lines, Kenya Airways, KLM, Korean Air, Middle East Airlines, Saudia, TAROM, Vietnam Airlines