United Air Lines, Inc., trading as United Airlines (NASDAQ: UAUA), is a major airline of the United States. It is a subsidiary of UAL Corporation with corporate offices in Chicago at 77 West Wacker Drive, and its operations base in nearby Elk Grove Township. United's largest hub is O'Hare International Airport, where it has 650 daily departures. United also has hubs in Denver International Airport, Washington Dulles International Airport, San Francisco International Airport, and Los Angeles International Airport. Its largest maintenance hub is the Maintenance Operations Center at San Francisco International Airport.

As of July 31, 2006, United is the world's second largest airline by revenue-passenger-miles (behind American Airlines), third-largest by total operating revenues (behind Air France-KLM and American Airlines), and fourth-largest by total passengers transported (behind American Airlines, Delta Air Lines and Southwest Airlines). United has 56,000 employees and operates 395 aircraft.

On February 1, 2006, United emerged from Chapter 11 bankruptcy protection under which it had operated since December 9, 2002, the largest and longest airline bankruptcy case in the history of the industry.