The album was released in 1970 after the band had shortened its name from "The Chicago Transit Authority" following the release of their self-titled
debut album the previous year, in order to avoid legal action being threatened by the
actual mass-transit company. The official title of the album is
Chicago, although it came to be known as
Chicago II, keeping it in line with the succession of Roman numeral-titled albums that officially began with
Chicago III in 1971.
Chicago Transit Authority was a success, yet
Chicago is considered by many to be the group's breakthrough album, yielding three singles that made it into the top ten of the Billboard Hot 100, including "
Make Me Smile" (number 9), "
Colour My World" (number 7), and "
25 or 6 to 4" (number 4).
Chicago was released in January 1970 on Columbia Records and was an instant hit, reaching number 4 on the Billboard 200 in the United States and number 6 in the UK. Columbia Records was very active in promoting its quadraphonic four-channel surround-sound format in the mid-1970s, and nine of Chicago's first ten albums were made available in quad. The quad mix features elements not heard in the standard stereo mix, including additional guitar work from virtuoso
Terry Kath in "25 Or 6 To 4" and a different vocal take from Lamm in "Wake Up Sunshine," which reveals a different lyric in the song's last line. In 2002,
Chicago was remastered and reissued on one CD by Rhino Records with the single versions of "Make Me Smile" and "25 or 6 to 4" as bonus tracks. Rhino released a DVD-Audio version of the album in 2003, featuring both Advanced Resolution Stereo and 5.1 surround sound mixes. In 2016, British producer and musician
Steven Wilson remixed
Chicago from the original multitrack tapes. This version was released on January 27, 2017, by Rhino Records. A vinyl edition of the remix cut by Kevin Gray was released on August 11, 2017.
Robert Lamm stated in an interview that the album has been nominated for the Grammy Hall of Fame more than once. ==Musical style, writing, composition==