Gregory of Nazianzus (329-390 C.E.) has had an immeasurable influence on the Eastern and Western Christian traditions. Along with his homiletical, ecclesiastical, and literary achievements, Gregory's doctrine of the Trinity became the definitive expression of the orthodox faith in Greek Christian tradition, which caused him to be the only person other than John the Evangelist to be granted the title of `Theologian` by an ecumenical church council. As a testimony to Gregory's importance, he is the most cited author after the Bible in Byzantine Christian literature. Christopher Beeley's groundbreaking study-the first comprehensive treatment in modern scholarship-examines Gregory's doctrine of the Trinity in the full range of his theological and practical vision. Following an overview of Gregory's life and major theological works, Beeley examines Gregory's teaching on a vast range of subjects: the purification and illumination of the theologian