This book is an introduction to trinitarian theology as it developed from the late medieval period. John T. Slotemaker presents an overview of the central aspects of trinitarian theology by focusing on four themes: theological epistemology, the emanations in God, the divine relations, and the Trinity of persons. He does so by exploring a broad range of theological opinions on each subject and delineating the options that existed for medieval theologians from the early thirteenth century through the sixteenth. He argues that despite the diversity of opinion on a given subject, there is a normative theological center that grounds late medieval trinitarian theology. This center consists of theological developments involving the adoption of Peter Lombard Sentences as a theological textbook, the conciliar decisions of Lateran IV, and a shared Aristotelian philosophical background of Western trinitarian theology.