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.