A study of the history of heresy and rival forms of Christianity, arguing that the church must continue to defend what is true about Jesus.Our ongoing fascination with alternative Christianities is on display every time a never-before-seen gospel text is revealed, an archaeological discovery about Jesus makes front-page news, or anew work of fiction challenges the very foundations of the church. Now, in a timely corrective to this trend, renowned church historian Alister McGrath examines the history of subversive ideas, overturning common misconceptions that heresy is somehow more spiritual or liberating than traditional dogma. In so doing, he presents a powerful, compassionate orthodoxy that will equip the church to meet the challenge from renewed forms of heresy today.