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, Gregorys 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 Gregorys importance, he is the most cited author after the Bible in Byzantine Christian literature. Christopher Beeleys groundbreaking study-the first comprehensive treatment in modern scholarship-examines Gregorys doctrine of the Trinity in the full range of his theological and practical vision. Following an overview of Gregorys life and major theological works, Beeley examines Gregorys teaching on a vast range of subjects: the purification and illumination of the theologian; the human limitations and the divine possibilities of the knowledge of God; the unique identity of Christ; Gregorys dynamic understanding of "divinization"; and the distinctive place of the Holy Spirit in Christian theology. Beeleys expansive discussion culminates in Gregorys understanding of the Trinity as a whole, which proves to be the fundamental principle of all Christian doctrine and practice. Finally, Beeley identifies the Trinitarian shape and purpose of pastoral ministry, of which Gregory is also the seminal theorist in Christian tradition. Beeley offers new insights in several key areas, including the reinterpretation of the famous Theological Orations and Christological epistles within the larger framework of Gregorys corpus. Long eclipsed in twentieth-century scholarship, Gregorys doctrine is now brought into full view as the major Greek witness to the Trinity as the governing principle and the main interpretive framework of the Christian life.