United Airlines dates to 1929, when William E. Boeing (1881–1956), Frederick B. Rentschler (1887–1956), and their associates founded United Aircraft Transport Corporation, a conglomerate of both aircraft manufacturing and air transport. By 1930 it had acquired four mail carriers—Boeing Air Transport (formed in 1927), Pacific Air Transport (1926), Varney Air Lines (1926), and National Air Transport (1925)—and in 1931 established United Airlines, Inc., in Chicago as a holding company providing an umbrella management for the four operating divisions.

United Polaris Business:

The Polaris seat converts into a 6' 6" flatbed in a 1-2-1 configuration or a 1-1-1 configuration, providing all-aisle access for every seat. The seat boasts multiple storage areas, mood lighting, multiple charging ports, lumbar support, and improved dining and amenity services. United Polaris Business passengers check in at separate counters and can use priority security screening where available. In-flight services include pre-departure beverages, table linens and multi-course meals.

United Premium Plus:

United Premium Plus is United's premium economy product, that is being retrofitted on wide-body international aircraft. United Premium Plus seating offers more space, comfort and amenities compared to United Economy or Economy Plus, and offers upgraded dining on china dinnerware, free alcoholic beverages, a Saks Fifth Avenue blanket and pillow, an amenity kit and more.

Transcontinental:

United premium transcontinental service is offered on transcontinental flights between Newark and Los Angeles or San Francisco and between Boston and San Francisco. The premium cabin also features international-style catering, while all seats have access to inflight wi-fi, on-demand entertainment, and power outlets. Business-class passengers also have access to the United Club at Newark, Boston, Los Angeles, and San Francisco.

United First:

United First seats on narrowbody aircraft have a 38-inch (97 cm) seat pitch, while United First seats on re-configured domestic Boeing 777-200 aircraft feature fully-flat-bed seats. Passengers receive priority boarding and baggage handling, pre-departure beverages, complimentary meals and separate check-in desks.

Economy Plus:

United Economy Plus is available on all aircraft. Economy Plus seats are located in the front few rows and exit rows of the economy cabin and have 2 inches (5.1 cm) more recline and at least 5 to 6 inches (13 to 15 cm) of additional seat pitch totaling 4 to 7 inches (10 to 18 cm) of recline (aircraft dependent) and 35 to 37 inches (89 to 94 cm) of pitch. Economy Plus is complimentary for all MileagePlus Premier members. Premier 1K, Platinum and Gold members may select an Economy Plus seat when booking, while silver members can select an Economy Plus seat at check-in

Economy:

United Economy is available on all aircraft, and usually have a pitch of 31 inches (30 inches on aircraft refurbished with Slimline seats, and 32 inches on Boeing 787s) and a recline of 2–5 inches. All economy seats feature an adjustable headrest and some form of entertainment, ranging from AVOD, inflight wi-fi, personal device entertainment, or DirecTV. Food and snacks are available for purchase on domestic, Caribbean, and some Latin America flights. These include snacks, fresh meals, and snack boxes, depending on flight time and distance. Meals are complimentary on all other international flights. Beverages and small snacks are complimentary in economy class on North America flights. Alcoholic beverages are available for purchase on North America flights but are complimentary on long-haul international flights.

Basic Economy:

Basic Economy is available on select routes and in addition to standard fares. Intended to be United's lowest fare, Basic Economy fares provide most of the same inflight services and amenities with standard United Economy Class. With Basic Economy, group/family seating, seat selection/upgrades and bringing full-sized carry-on bags are not allowed. When booking online, it is clearly marked - with a user prompt to confirm the user is booking a Basic Economy fare.

United Airlines operated a fleet of 834 aircraft with an additional 49 aircraft planned; all of which are either Boeing or Airbus. United has eight hubs, with Chicago–O'Hare being its largest in terms of passengers carried and the number of departures. It is a founding member of the Star Alliance, the world's largest airline alliance with a total of 28 member airlines. Regional service is operated by independent carriers under the brand name United Express.