Wikipedia
AAdvantage is the frequent flyer program of American Airlines. Launched May 1, 1981, it was the second such loyalty program in the world (after the first at Texas International Airlines in 1979), and remains the largest with more than 67 million members as of October 2011.
Miles accumulated in the program allow members to redeem tickets, upgrade service class, or obtain free or discounted car rentals, hotel stays, merchandise, or other products and services through partners. The most active members, based on the amount and price of travel booked, are designated AAdvantage Gold, AAdvantage Platinum, and AAdvantage Executive Platinum elite members, with privileges such as separate check-in, priority upgrade and standby processing, or free upgrades. They also receive similar privileges from AA's partner airlines, particularly those in Oneworld. AAdvantage co-branded credit cards are also available and offer other benefits. These cards are issued by CitiCards, subsidiary of Citigroup in the United States and by MBNA in the United Kingdom.
AAdvantage allows one-way redemption, starting at 5,000 miles.