What are individuals? How can they be identified? These are crucial questions for philosophers and scientists alike. Criteria of seem to differ markedly between metaphysics and the empirical sciences - and this might well explain why no work has hitherto attempted to relate the contributions of metaphysics, physics and biology on this question. This timely volume brings together various strands of research into 'individuality', examining how different sciences handle the issue, and reflecting on how this scientific work relates to metaphysical concerns. The collection makes a major contribution to clarifying and overcoming obstacles to the construction of a general conception of the individual adequate for both physics and biology, and perhaps even beyond.