Contemporary theology is driven by a quest to make the doctrine of the Trinity "relevant" to a wide variety of concerns. Books and articles abound on the Trinity and personhood, the Trinity and ecclesiology, the Trinity and gender, the Trinity and marriage, the Trinity and societal relations, the Trinity and politics, the Trinity and ecology, etc. Recently a number of theologians have suggested that a doctrine of the Trinity may provide the key to a Christian theology of religions. The purpose of this study is to evaluate critically the claim that a proper understanding of "the Trinity" provides the basis for a new understanding of religious diversity. Drawing upon the trinitarian theology of Augustine (principally De Trinitate), I critically examine the trinitarian doctrine in Mark Heim0́9s trinitarian theology of multiple religious ends, Amos Yong's pneumatological theology of religions, Jacques Dupuis' Christian theology of religious pluralism and Raimundo Panikkar's trinitarian account of religious experience (along with Ewert Cousins' efforts to link Panikkar's proposal to the vestige tradition). My Augustinian assessment is structured around three trinitarian issues in the Christian theology of religions: (1) the relationship of the "immanent" and the "economic"+ Trinity, (2) the relations among the divine persons (both ad intra and ad extra) and (3) the vestigia trinitatis. In conversation with Augustine, I argue (1) that there is good reason to question the claim that the "Trinity" represents the key to a new understanding of religious diversity, (2) that current "use" of trinitarian theology in the Christian theology of religions appears to be having a deleterious effect upon the doctrine, and (3) that the trinitarian problems I document in the theology of religions also encumber attempts to relate trinitarian doctrine to a variety of other contemporary issues including personhood, ecclesiology, society, politics and science. I further argue that contemporary theology is driven by a problematic understanding of what it means for a doctrine of the Trinity to be "relevant" and that Augustine challenges us to rethink the "relevancy" of trinitarian doctrine.