Gaven Kerr provides the first book-length study of St. Thomas Aquinas's much neglected proof for the existence of God in De Ente et Essentia Chapter 4. He offers a contemporary presentation, interpretation, and defense of this proof, beginning with an account of the metaphysical principlesused by Aquinas and then describing how they are employed within the proof to establish the existence of God. Along the way, Kerr engages contemporary authors who have addressed Aquinas's or similar reasoning. The proof developed in the De Ente is, on Kerr's reading, independent of many of the other proofs in Aquinas's corpus and resistant to the traditional classificatory schemes of proofs of God. By applying a historical and hermeneutical awareness of the philosophical issues presented by Aquinas'sthought and evaluating such philosophical issues with analytical precision, Kerr is able to move through the proof and evaluate what Aquinas is saying, and whether what he is saying is true.By means of an analysis of one of Aquinas's earliest proofs, Kerr highlights a foundational argument that is present throughout the much more commonly studied Thomistic writings, and brings it to bear within the context of analytical philosophy, showing its relevance to the contemporaryreader.