This complete yet concise reference work provides scholars and students with accurate interpretations of the ways in which Thomas Aquinas (1225-1274) used important theological terms. Aquinas, a theologian and philosopher in the Roman Catholic Church, sought to reconcile faith and reason, philosophy and Christianity. He discussed many theological topics in his extensive writings and became one of the most important theologians of the Middle Ages. His influence continues to be pervasive today and his thought is of major interest to both Roman Catholics and Protestants. This volume is an introduction to the theology of Aquinas and provides direction to the most important features of his theological thought. It is a reliable guide to his teaching with entries arranged alphabetically and key Latin terms cross-indexed. For each entry, the main points of the teaching are sketched along with the passages in Aquinas where his views are found. Resources for further study are also provided. An extensive bibliography to secondary literature enhances the value of this key resource for the study of one of the major theologians in the history of theology.