Marcellus of Ancyra (ca. 285-374) was a controversial figure in the Trinitarian debate after Nicaea. He has often been written off as the odd heretic who misunderstood the teaching of the Council of Nicaea and taught that the Godhead temporarily expanded into a Dyad, and then into a Triad, but would, at the end of time, contract once again to a Monad. In other words, he supposedly taught that the Trinity was a temporary phenomenon. But, according to the author of this volume, Marcellus was not primarily concerned with speculation on the Trinity; rather his concern was with monotheism, and with the full humanity of Christ. Here, Joseph T. Lienhard, S.J., studies the so-called Arian controversy of the fourth century from one well-defined angle: Marcellus and his influence. The book shows that Marcellus, far from being isolated, was part of a larger theological tendency. Among those who sympathized with him were Athanasius of Alexandria, much of the western church, and bishops in Asia Minor and Egypt. Lienhard begins by studying Marcellus's life and the history of modern scholarship on Marcellus. He then examines the Arian controversy in terms of two theological systems in conflict, called "miahypostatic theology" and "dyohypostatic theology," depending on whether a system held that God is best called one hypostasis or two. Lienhard provides a complete analysis of Marcellus's theology, using only the certainly authentic works of his that survive, and traces the reactions to his teaching-from those who remained sympathetic to him, to those who rejected his theology outright, and finally to those who partially accepted his theses. This book is part of a larger project among scholars to reexamine and rewrite the history of the Arian controversy in the fourth century.