Arguably the most influential work of systematic theology in the history of Christianity, Thomas Aquinas' Summa Theologiae has shaped all subsequent theology since it was written in the late thirteenth century. This Companion features essays from both specialists in Aquinas' thought and from constructive contemporary theologians to demonstrate how to read the text effectively and how to relate it to past and current theological questions. The authors thoroughly examine individual topics addressed in the Summa, such as God, the Trinity, eternity, providence, virtue, grace, and the sacraments,...