Foster was a major contributor to Chicago's career in the early and middle 1980s, having worked as the band's producer on "Chicago 16" (1982), "Chicago 17" (1984 - their biggest selling multi-platinum album), and "Chicago 18" (1986). As was typical of his producing projects from this time period, Foster was a cowriter on songs such as the US Chart No. 1 hit "Hard to Say I'm Sorry", "Love Me Tomorrow" (US No. 22), "Stay the Night" (US No. 16), and "You're the Inspiration" (US No. 3). These four songs were cowritten with the band's bassist Peter Cetera. Foster also helped Cetera co-write (along with Cetera's wife Diane Nini) his US No. 1 solo hit "Glory of Love" in 1986. Foster cowrote Kenny Loggins's songs "Forever" (US No. 40), from the 1985 album "Vox Humana", and "Heart to Heart" (US No. 15), from the 1982 album "High Adventure". Foster also worked with country singer Kenny Rogers on the hit albums "What About Me?" (1984) and "The Heart of the Matter" (1985), the latter of which featured "The Best of Me" a song co-written by Richard Marx that was covered by Cliff Richard in 1989, resulting in a number-two UK hit.