Originally released in 1970 on the album "Chicago II", “25 or 6 to 4” was written by Robert Lamm and produced by James William Guercio. The song reached #4 on the Billboard Hot 100 and became one of Chicago’s signature rock tracks, known for its driving guitar riff and horn section. It has been re-recorded multiple times by the band, remaining a staple of their live performances for decades.