In the intellectual tradition of the Christian faith, few thinkers have had a more profound effect upon both the nature of theology and the materials with which it deals than Thomas Aquinas. A knowledge of his major work the Summa Theologiae is, therefore, necessary for the student of theology, as well as for anyone concerned with the Western intellectual tradition. This, together with the immensity, length, and difficulty of the Summa, make a Reader's Guide valuable, even crucial, to a student's first exposure to the work. To address the needs of undergraduates, Stephen Loughlin presents the basic principles that underlie the Summa Theologiae both as a whole and with respect to its three parts, and the varying treatises found within them.