This article is a critical assessment of Pannenberg's trinitarian approach in his Systematic Theology. In particular it raises the questions of how far Pannenberg's emphasis on the Trinity affects the practice of theology and of how the theologian should understand his or her task in the light of the being and work of the triune God. It argues that there is an uneasy tension between Pannenberg's commitment to thoroughgoing trinitarianism on the one hand and his commitment to a rational theology that takes account of the modern age. This tension can be seen most clearly in Pannenberg's treatment of christology, faith and theological method. It is at these points, where modern thinking has often been so critical with traditional theology, that Pannenberg's trinitarian commitments are not deployed as consistently or penetratingly as elsewhere.