After leaving school at 16, Book became an apprentice bricklayer and played amateur football as an inside-forward for Peasedown Miners, until he was called up for national service in 1952. While playing for his army team Book converted to the full-back position and had a trial with Chelsea courtesy of a recommendation from army team-mate Frank Blunstone, but was not taken on. Following the completion of his national service, Book returned his bricklaying job in Bath and started playing for Frome Town. During the 1955–56 season Frome suffered financial difficulties, and sent letters to all their players permitting them to leave if they wished. Book showed his letter to a work colleague, who played for Bath City of the Southern League. He in turn informed the Bath chairman, and Book signed for the club in January 1956. He spent seven and a half years at Bath, becoming captain in the latter part of his Bath career, and winning the Southern League title in 1960. In the 1962 close season, Malcolm Allison became Bath manager, beginning a long association between the two.
Upon his return to England, Book was signed for Plymouth by Allison for a fee of £1,500, and Book entered the Football League for the first time at the age of 30, though Plymouth believed him to be 28 - Allison had advised Book to doctor his birth certificate as he thought the Plymouth board would not pay £1,500 for a 30 year old. After making 81 league appearances, Book followed Malcolm Allison again to Manchester City two years later, this time for a transfer fee of £17,000. Manager Joe Mercer was initially reluctant to spend such a fee on a player over 30 years old, but was persuaded after Allison pointed out that Mercer's career had included a successful move at a similar age, when he joined Everton from Arsenal aged 32.
Book prospered under the management of Mercer and Allison. He made his Manchester City debut in the opening match of the 1966–67 season, a 1–1 draw with Southampton, and became a near-permanent fixture in the team. In his first season at the club he missed just one game, becoming the inaugural winner of the club's Player of the Year award in a season in which the club consolidated their position following promotion.
In the 1967 close season, Book was named captain following the transfer of previous captain Johnny Crossan to Middlesbrough, and was henceforth nicknamed Skip by his teammates. His first season as captain was a very successful one, leading Manchester City to their second league championship and playing every game. An Achilles injury sidelined Book for the first four months of the 1968–69 season, but he returned to the team in time for the start of their FA Cup run. In the week preceding the cup final, Book was named the 1969 Football Writers' Association Footballer of the Year Award, sharing the accolade with Dave Mackay. The following Saturday Manchester City played Leicester in the FA Cup final. Manchester City won 1–0, and captain Book lifted the trophy. The following season City became the first team to win a European and domestic trophy in the same season, the European Cup Winners' Cup and the League Cup. Book retired from playing in 1974, passing the captaincy to Colin Bell. He made 242 football league appearances for the club, and is City's most successful captain in terms of trophies won.
As of 2008 Book is retired, but holds two honorary positions; he is Honorary President of Manchester City and Life President of the Manchester City Official Supporters Club. He was inducted into Manchester City's Hall of Fame in January 2004.