Book excerpt: There have been twenty-one universal gatherings 'ecumenical councils' of the Catholic Church. The first opened in 325, the last closed in 1965, and the names of many ring out in the history of the church: Nicea, Chalcedon, Trent, Vatican II. Though centuries separate the councils, each occurred when the church faced serious crises, sometimes with doctrinal matters, sometimes with moral or even political matters, and sometimes with discerning the church's relation to the world. The councils determined much of what the Catholic Church is and believes. Additionally, many councils impacted believers in other Christian traditions and even in other faiths. In this accessible, readable, and yet substantial account of the councils Joseph Kelly provides both the historical context for each council as well as an account of its proceedings. Readers will discover how the councils shaped the debate for the following decades and even centuries, and will appreciate the occasional portraits of important conciliar figures from Emperor Constantine to Pope John XXIII.