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 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, making the text accessible to students of all levels. They further discuss the contextual, methodological, and structural issues surrounding the Summa, as well as its interaction with a variety of religious traditions. This volume will not only allow readers to develop a comprehensive multi-perspectival understanding of Aquinas' main mature theological work, but also promote a meaningful dialogue about the vital role of the Summa in theology today.