This collection of essays by leading philosophers of physics was first published in 2000, and offers philosophical perspectives on two of the central elements of modern physics, quantum theory and relativity. The topics examined include the notorious 'measurement problem' of quantum theory and the attempts to solve it by attributing extra values to physical quantities, the mysterious non-locality of quantum theory, the curious properties of spatial localization in relativistic quantum theories, and the problem of time in the search for a theory of quantum gravity. Together the essays represent some of the last decade's research in philosophy of physics, particularly interestingly within the philosophy of quantum theory.