As a resource for students in colleges, universities, and seminaries, as well as for teachers of the perennial tradition and interested general readers, occupies a unique place. It offers precise, yet clear and understandable accounts of well over a thousand key philosophical terms, richly cross-referenced. It also explains significant terms from other philosophical movements with which Thomism (and the Catholic intellectual tradition more generally) has engaged—either through debate or through judicious and creative incorporation. Moreover, it identifies a number of theological and doctrinal expressions to which perennial philosophy has contributed. Finally, it provides a comprehensive bibliography of works by Aquinas in English, expositions and discussions of perennial themes, and representative examples from the writings of all philosophers and theologians mentioned in dictionary entries.