The papers in this volume address fundamental, and interrelated, philosophical issues concerning modality and identity, issues that have not only been pivotal to the development of analytic philosophy in the twentieth century, but remain a key focus of metaphysical debate in the twenty-first. How are we to understand the concepts of necessity and possibility? Is chance a basic ingredient of reality? How are we to make sense of claims about personal identity? Do numbers require distinctive identity criteria? Does the capacity to identify an object presuppose an ability to bring it under a sortal concept? Rather than presenting a single, partisan perspective, Identity and Modality enriches our understanding of identity and modality by bringing together papers written by leading researchers working in metaphysics, the philosophy of mind, the philosophy of science, and the philosophy of mathematics. The resulting variety of perspectives correspondingly reflects both the breadth and depth of contemporary theorizing about identity and modality, each paper addressing a particular issue and advancing our knowledge of the area. This volume will provide essential reading for graduate students in the subject and professional philosophers.