Thomas Aquinas and Karl Barth are often taken to be two of the greatest theologians in the Christian tradition. This book undertakes a systematic comparison of them through the lens of five key topics: (1) the being of God, (2) Trinity, (3) Christology, (4) grace and justification, and (5) covenant and law. Under each of these headings, a Catholic portrait of Aquinas is presented in comparison with a Protestant portrait of Barth, with the theological places of convergence and contrast highlighted. This volume combines a deep commitment to systematic theology with an equally profound commitment to mutual engagement. Understood rightly and well, Aquinas and Barth contribute powerfully to the future of theology and to an ecumenism that takes doctrinal confession seriously while at the same time seeking unity among Christians. Contributors: John R. BowlinHolly Taylor CoolmanRobert W. JensonKeith L. JohnsonGuy Mansini, O.S.B.Amy MargaBruce L. McCormackRichard Schenk, O.P.Joseph P. WawrykowThomas Joseph White, O.P.