Heidegger thought seriously about the implications of human coexistence, and this book shows that conceptions of trust and responsibility that lie at the very heart of morality are to be found in the sketch of Mitsein--our being together with one another in the world--offered in Being and Time. Written by one of the preeminent interpreters of Heidegger, this book is an important statement about the basis of human sociality that is a major contribution to the continuing debates about Heidegger in particular, and ethics in general.