This book introduces Thomas Aquinas's moral, economic, and political thought, differentiating between philosophy (justice) and theology (charity) within each of the three branches of Aquinas's theory of human living. It shows how Aquinas's thought offers an integrated vision for Christian participation in the world, equipping readers to apply their faith to the complex moral, economic, and political problems of contemporary society. Written in an accessible style by an experienced educator, the book is well-suited for use in a variety of undergraduate courses and provides a foundation for understanding Catholic social teaching.