This is the first full-length study of the doctrine of the Trinity from the standpoint of analytic philosophical theology. William Hasker reviews the evidence concerning fourth-century pro-Nicene trinitarianism in the light of recent developments in the scholarship on this period, arguing for particular interpretations of crucial concepts. He then reviews and criticizes recent work on the issue of the divine three-in-oneness, including systematic theologians such as Barth, Rahner, Moltmann, and Zizioulas, and analytic philosophers of religion such as Leftow, van Inwagen, Craig, and Swinburne. In the final part of the book he develops a carefully articulated social doctrine of the Trinity which is coherent, intelligible, and faithful to scripture and tradition.