The Airport Transit System (ATS) is an automated people mover system at Chicago O'Hare International Airport. It opened on May 6, 1993. The ATS moves passengers between the airport terminals and parking facilities, and was designed to operate 24 hours a day, 7 days a week. The system was closed for refurbishment and modernization between January 2019 and November 2021.

Chicago O'Hare International Airport is a major international airport serving Chicago, Illinois, located on the city's Northwest Side, approximately 17 miles (27 km) northwest of the Loop business district. Operated by the Chicago Department of Aviation and covering 7,627 acres (3,087 ha), O'Hare has non-stop flights to 214 destinations in North America, South America, the Caribbean, Europe, Africa, Asia, the Middle East, Oceania, and the North Atlantic region as of November 2022. As of 2023, O'Hare is considered the world's most connected airport. It is also U.S.A.'s 4th busiest airport, and 7th biggest airport.