Accelerating Expansion explores some of the philosophical implications of modern cosmology, focused on the significance that the discovery of the accelerating expansion of the Universe has for our understanding of time, geometry, and physics. The appearance of the cosmological constant in the equations of general relativity allows one to model universes in which space has an inherent tendency towards expansion. This constant, introduced by Einstein but subsequently abandoned by him, returned to centre stage with the discovery of the accelerating expansion. This pedagogically-oriented essay begins with a study of the most basic and elegant relativistic world that involves a positive cosmological constant, de Sitter spacetime. It then turns to the relatives of de Sitter spacetime that dominate modern relativistic cosmology. Some of the topics considered include: the nature of time and simultaneity in de Sitter worlds; the sense in which de Sitter spacetime is a powerful dynamical attractor; the limited extent to which observation can give us information about the topology of space in a world undergoing accelerated expansion; and cosmologists' favourite sceptical worry about the reliability of evidence and the possibility of knowledge, the problem of Boltzmann brains. "The book arrives at discussions of "no-hair" theorems, links to quantum mechanics, and Boltzmann brains. The references are extensive, and the book is accessible to advanced undergraduates and graduate students. Highly recommended. Advanced undergraduates through faculty; professionals." -- Choice " Accelerating Expansion shows that taking de Sitter spacetime seriously generates remarkably interesting foundational questions that have been central to active discussions in mathematical physics. It introduces philosophers to some of the mathematical infrastructure designed to apply general relativity that has been developed over the last fifty years, in part through considering a case where it breaks break down." -- Chris Smeenk, The British Journal for the Philosophy of Science "In any case, none of this should detract from the fact that Belot's book will surely become the go-to resource, both for philosophers of physics and (ideally) philosophically-minded physicists, on all things de Sitter. We very much hope that the book will promulgate an expanding research programme in the philosophy of physics, and we look forward to seeing its fruits in the years to come." -- Franciszek Cudek, Springer Gordon Belot, Lawrence Sklar Collegiate Professor of Philosophy, University of Michigan Gordon Belot studied at the University of Toronto, Cambridge University, and the University of Pittsburgh. He has taught at Princeton University, New York University, the University of Pittsburgh, and the University of Michigan, where he is currently the Lawrence Sklar Collegiate Professor of Philosophy. His book Geometric Possibility won the Lakatos Award. He has held fellowships from the Social Sciences and Humanities Research Council, the National Science Foundation, the American Council of Learned Societies, and the Center for Advanced Study in the Behavioral Sciences, and is a fellow of the American Association for the Advancement of Science.