The Early Heidegger and Medieval Philosophy is a major interpretive study of Heidegger's complex relationship to medieval philosophy. S. J. McGrath's contribution is historical and biographical as well as philosophical, examining how the enthusiastic defender of the Aristotelian-Scholastic tradition became the great destroyer of metaphysical theology. This book provides an informative and comprehensive examination of Heidegger's changing approach to medieval sources--from the seminary studies of Bonaventure to the famous phenomenological destructions of medieval ontology. McGrath argues that the mid-point of this development, and the high point of Heidegger's reading of medieval philosophy, is the widely neglected habilitation thesis on Scotus and speculative grammar. He shows that this neo-Kantian retrieval of phenomenological moments in the metaphysics of Scotus and Thomas of Erfurt marks the beginning of a turn from metaphysics to existential phenomenology. McGrath's careful hermeneutical reconstruction of this complex trajectory uncovers the roots of Heidegger's critique of ontotheology in a Luther-inspired defection from his largely Scholastic formation. In the end McGrath argues that Heidegger fails to do justice to the spirit of medieval philosophy. The book sheds new light on a long-debated question of the early Heidegger's theological significance. Far from a neutral phenomenology, Heidegger's masterwork, Being and Time, is shown to be a philosophically questionable overturning of the medieval theological paradigm.