In November 1973, Manchester City manager Johnny Hart resigned due to ill health, and Book took temporary responsibility for first-team affairs, and was named assistant manager when Ron Saunders became the next permanent manager. At this point Book retired from playing to concentrate on management. Saunders was sacked after less than six months, and Book again took on the caretaker role, and was appointed permanent manager one game later. The first notable victory of Book's management was a 1–0 Manchester derby win, best known for the back-heel scored by Denis Law. Book's first full season as manager resulted in an eighth-place finish, an improvement upon the previous season, when the team finished 14th. In 1976, Book's City side won the League Cup, making him the first person to win the competition as both player and manager. City continued their run of form into the following season, enjoying an impressive league campaign where they finished in second place, only a point behind winners Liverpool. City were playing entertaining football in the late 1970s and regularly drawing crowds at Maine Road in excess of 40,000. Book remained manager until 1979, when he was replaced by his former mentor Malcolm Allison. He then became a loyal stalwart to the club in several other roles until 1997, including as caretaker manager again in 1993. He joined Huddersfield Town in 1997 as Chief Scout under Brian Horton.