THE THEOLOGY OF PAUL TILLICH examines Tillich's main theological work, the three-volume Systematic Theology, against the background of Tillich's developing theological thought since his studies around 1900. While the Systematic Theology emerged from lectures Tillich gave at Union Theological Seminary in New York from 1936 onwards, his lectures on "Advanced Problems in Systematic Theology" take up considerations that go back to his first drafts of a systematic theology from 1913 and his dogmatic lectures from Germany in the 1920s. The Systematic Theology that Tillich published in the U.S. cannot, therefore, be understood without including his German dogmatic drafts, an area of Tillich research that has previously been underrepresented in English scholarship. In Part I, the development of Tillich's theology from the time of his studies in Berlin, Tübingen, Halle, and again in Berlin up to his immigration to the United States in 1933 is examined by tracing his revelation-theological concept of religion within the context of theological developments in Germany at the time. Part II is devoted to a systematic perspective on the doctrine of God, Christology, pneumatology, and a theology of religions in the late Systematic Theology. This presentation of Tillich's theology is framed by a prologue and an epilogue. While the former places his theological thinking within the history of the development of modern Protestant theology, the latter identifies problematic elements within Tillich's theology that must be overcome in a post-pluralist world. The result is a concise introduction to Paul Tillich's thought in the context of twentieth-century Protestant theology and a clear direction for responsible appropriations of Tillich's theology today.