This book is a systematic reconstruction of Heidegger's account of time and temporality in Being and Time. The author locates Heidegger in a tradition of 'temporal idealism' with its sources in Plotinus, Leibniz, and Kant. For Heidegger, time can only be explained in terms of 'originary temporality', a concept integral to his ontology. Blattner sets out not only the foundations of Heidegger's ontology, but also his phenomenology of the experience of time. Focusing on a neglected but central aspect of Being and Time, this book will be of considerable interest to all students of Heidegger both inside and outside philosophy.