Chicago is an American rock band formed in 1967 in Chicago, Illinois. Initially emerging from a university scene, the band is characterized by its "rock and roll band with horns" sound, combining elements of rock, jazz, pop, R&B, and classical music. The original lineup consisted of trumpet player Lee Loughnane, saxophonist Walter Parazaider, guitarist Terry Kath, trombonist James Pankow, drummer Danny Seraphine, keyboardist Robert Lamm, and bassist Peter Cetera. The group went through several names before officially adopting The Chicago Transit Authority in 1968, which was later shortened to Chicago in 1969.

Chicago's debut album, released under the name Chicago Transit Authority, showcased extended jams and intricate arrangements, producing popular singles such as "Does Anybody Really Know What Time It Is?" and "Beginnings." Their second album, Chicago II, marked a breakthrough for the band with hits that included "Make Me Smile" and "Color My World." Throughout the 1970s, Chicago released multiple albums a year, establishing themselves as a dominant force in rock music.

In 1981, Chicago began a new phase after signing with Warner Brothers and collaborating with producer David Foster. This era introduced new members, including Bill Champlin and Chris Pinnick, and resulted in successful singles like "Hard to Say I’m Sorry/Get Away” and "Love Me Tomorrow." Their 1984 album, Chicago 17, achieved significant commercial success, featuring well-received tracks such as “You’re the Inspiration” and “Hard Habit to Break.” The band continued to perform well into the late 1980s, achieving another number-one hit with “Look Away” from their album Chicago 19 in 1988.

With over 22 gold albums, 18 platinum albums, and more than 100 million records sold worldwide, Chicago ranks among the best-selling American bands in history. They have achieved 21 top ten singles and five number-one albums on the Billboard charts. Notably, they became the first rock act to sell out Carnegie Hall for a week in 1971, demonstrating their widespread popularity.

Despite several lineup changes, key members such as Lamm, Loughnane, and Pankow have remained constant, while Parazaider, who retired in 2017, has been open about his Alzheimer's diagnosis. After the death of guitarist Terry Kath in 1978, the band has had various musicians succeed him over the years, including Jason Scheff, who replaced Cetera in 1985, and Tris Imboden, who took over for Seraphine in 1990.

Chicago's achievements have been recognized with numerous awards, including a Grammy Award for their hit “If You Leave Me Now” and induction into the Grammy Hall of Fame for their debut album. The original lineup was inducted into the Rock and Roll Hall of Fame in 2016, and the group received a Grammy Lifetime Achievement Award in 2020.

The band remains active in the music industry, continuing to write, record, and tour. Their most recent release, Chicago at Symphony Hall, came out in 2015. In addition, a CNN documentary titled Now More Than Ever: The History of Chicago aired in 2017, reflecting the band's historical significance and ongoing relevance.

As one of the most successful American rock bands, Chicago is second only to the Beach Boys in total record sales. They have established a lasting legacy in the music world, marked by their distinctive sound and extensive influence on popular music.