Fr John Behr is the Dean of St Vladimir's Seminary and Professor of Patristics, teaching courses in patristics, dogmatics and scriptural exegesis at the seminary, and also at Fordham University, where he is the Distinguished Lecturer in Patristics. His early work was on issues of asceticism and anthropology, focusing on St Irenaeus of Lyons and Clement of Alexandria. After spending almost a decade in the second century, Fr John began the publication of a series on the Formation of Christian Theology, and has now reached the fifth and sixth centuries. He has recently completed an edition and translation of, and introduction to, the remaining texts of Diodore of Tarsus and Theodore of Mopsuestia. He has also published a synthetic presentation of the theology of the early centuries, focused on the mystery of Christ.