United Airlines, Inc. is a major American airline headquartered at the Willis Tower in Chicago, Illinois. United operates an extensive domestic and international route network across the United States and all six inhabited continents primarily out of its eight hubs, with Chicago–O'Hare having the largest number of daily flights and Denver carrying the most passengers in 2023. Regional service is operated by independent carriers under the brand name United Express.

Star Alliance is the world's first global airline alliance. Founded on 14 May 1997, it is headquartered on the grounds of Frankfurt Airport in Frankfurt, Germany, with a subsidiary management company in Singapore. Star Alliance is also the world's largest airline alliance by market share as of April 2024, with 17.4% of the market share, compared to 13.7% of SkyTeam and 11.9% of Oneworld.