Who am I, and what am I? The question is one asked through the ages, answered in various ways in different disciplines. Identity is a matter of intellectual interest but also of personal and practical interest, attracting attention and stimulating controversy outside the ranks of the specialists. This volume offers a comparison and cross-fertilization of insights and theories from various disciplines in which identity is a key concept.Identity contains essays by six internationally famous contributors, focusing on different facets of identity from the viewpoint of their various disciplines. Two philosophers, Bernard Williams and Derek Parfit, discuss, respectively, numerical identity (when can we say that two phenomena observed at different times are one and the same thing?) and personal identity (how far can the concept of `I' be stretched, and does it always matter whether we can say if that would still be me?). Henry Harris looks at philosophical discussions of identity from the persopective of an experimentalist, and discusses whether philosophical thought-experiments have any basis in scientific reality. The essays that follow offer perspectives from outside philosophy: Michael Ruse considers homosexual identity and to what extent it is reasonable to claim that homosexuality is a social construct. Terence Cave looks at personal identity through the eye of literature and fiction, and portrays idetnity as generated through the narratives that one weaves about oneself or about other people. Finally, Anthony D Smith looks at national identities and how they are formed, analysing how this process is shaped by the interplay of cultural inheritance, political expediency, and myth.