Delta Air Lines, Inc. is a major airline in the United States headquartered in Atlanta, Georgia, operating nine hubs, with Hartsfield–Jackson Atlanta International Airport being its largest in terms of total passengers and number of departures. With its regional subsidiaries and contractors operating under the brand name Delta Connection, Delta has over 5,400 flights daily and serves 325 destinations in 52 countries on six continents. Delta is one of the oldest still-operating commercial airlines in the U.S., having commenced passenger operations in 1929. At the turn of the 21st century it was a founding member of SkyTeam, an airline alliance. The airline ranks first in revenue and brand value among the world's largest airlines, and second by number of passengers carried and passenger miles flown.