Peter Unger here presents a fascinating new multidimensional account of the determinants of personal identity. He explains why many influential contemporary philosophers have underrated the importance of physical continuity to survival of the person, shedding new light on the work of such figures as Sidney Shoemaker and Derek Parfit. In the course of his discussion Unger produces a novel and controversial account of the relation of identity and practical human concerns, and explores the implications of his theory for questions of value, certain questions of morality, and the theory of rationality.