Arianism has been called the "archetypal Christian heresy": it denies the divinity of Christ. This masterly study of Arius by Rowan Williams, made available again and augmented with a new introduction and a fresh conclusion, provides the finest examination of Arianism ever written. In exploring the background and mind of Arius, Williams argues that this classic "heretic" was in fact a dedicated theological conservative whose concern was to defend the free and personal character of the Christian God. According to Williams, Arius's heresy grew out of his attempt to unite traditional biblical language with radical philosophical ideas and techniques and involved, from the start, issues of authority in the church. Thus, the crisis of the early fourth century was not only about the doctrine of God but also about the relations between emperors, bishops, and ascetical "charismatic" teachers in the church's decision-making. Williams raises the vital wider questions of how heresy is defined and how certain kinds of traditionalism transform themselves into heresy. Arius is widely considered to be Williams's magnum opus. Long out of print and never before available in paperback, the reissue of this extremely important book -- in a form and at a price which will be attractive to non-specialists as well as to scholars -- is a major publishing event.