United Continental Holdings, Inc., commonly referred to as United, is a major American airline headquartered in Chicago, Illinois. It is the world's third-largest airline when measured by revenue, operates a comprehensive domestic and international route network, and has significant presence in the Asia-Pacific region. In the late 1920s, just prior to the use of the United Airlines name, The Boeing Company, currently one of the world's largest aircraft manufacturers, operated a predecessor airline. United was previously known as United Air Lines (UAL).
United is a founding member of Star Alliance, the world's largest global airline alliance. Regional service is operated by independent carriers under the brand name United Express. Its main competitors are American Airlines, Delta Air Lines, and Southwest Airlines.
United operates out of nine airline hubs located in Chicago, Denver, Guam, Houston, Los Angeles, Newark, San Francisco, Tokyo and Washington, D.C. Chicago-O'Hare is United's largest hub, both in terms of passengers carried annually (16.6 million in 2016) and in terms of departures 181,488 in 2016). This passed George Bush Intercontinental in Houston, which carried 15.5 million with 178,019 departures. The company employs over 86,000 people while maintaining its headquarters in Chicago's Willis Tower (formerly known as Sears Tower). Through the airline's parent company, United Continental Holdings, it is publicly traded under NYSE: UAL with a market capitalization of over $18 billion as of September 2014. United operates maintenance bases in Cleveland and Orlando in addition to the maintenance locations located at United's hubs. Wikipedia