Lucid, absorbing, and original, this book defends the theory that the material world is composed of temporal as well as spatial parts. Along the way, it addresses many topics on the metaphysics of time and identity. These include the status of past and future objects, the nature of motion and change, the existence of composite objects, and examples involving two things in the same place at the same time. "Theodore Sider's excellent book provides an extremely lucid, persuasive, and detailed defense of the four-dimensionalist position, one that poses formidable challenges to the three-dimensionalist...Sider adds powerful new considerations of his own creation to the existing stockpile, which no doubt will engender a flurry of serious philosophical scrutiny in the literature to come...As a result, Sider arrives at an extraordinarily thoughtful, informative, and balanced assessment of the debate over persistence from which misleading rhetoric is largely absent...For many years to come, this book is sure to be the locus classicus with respect to which all those engaged with the literature on persistence must position themselves." --The Philosophical Review Theodore Sider is in the Department of Philosophy, Rutgers University, New Jersey.