Chicago is an American rock band formed in 1967 in Chicago, Illinois. The self-described "rock and roll band with horns" began as a politically charged, sometimes experimental, rock band and later moved to a predominantly softer sound, generating several hit ballads. The group had a steady stream of hits throughout the 1970s and 1980s. Since at least 2008, Billboard has shown Chicago to be the "greatest of all time" American band in singles chart success, and since 2015, the "greatest of all time" American band in album chart success as well. Chicago is one of the longest-running and most successful rock groups, and one of the world's best-selling groups of all time, having sold more than 100 million records.

According to Billboard, Chicago was the leading singles charting group in the United States during the 1970s. They have sold over 40 million units in the U.S., with 23 gold, 18 platinum, and 8 multi-platinum albums. They have had five number-one albums on the Billboard 200 and 19 top-ten singles on the Billboard Hot 100. They were inducted into the Rock and Roll Hall of Fame in 2016. In 2017, original band members Peter Cetera, Robert Lamm, and James Pankow were elected to the Songwriters Hall of Fame for their songwriting efforts as members of the music group.