This book sets out a new theory of the unity of objects. The author introduces the reader to the central problems faced by philosophical accounts of identity, problems which can, to a large extent, be solved using the theory developed in the book. In his consideration of the vexed issue of personal identity, the author argues that in our everyday thinking about persons we merge radically different kinds of notions. He suggests that our assessment of sameness of person is not founded on any determinate concept of person. Many central topics in epistemology and metaphysics are addressed in the course of the book and the author provides an original examination of each: the nature of physical objects, the metaphysics of possible worlds, the meaning of continuity in space and time and the nature of philosophical theorizing itself. The book is written in non-technical language and so will be of interest to the non-specialist philosopher.