This book concerns the philosophy of space and time, and its connection with the evolution of modern physics. As these are already the subjects of many excellent books and papers – the literature of the “absolute versus relational” debate – the production of yet another book may seem to require some excuse. I don't claim to defend a novel position in that controversy, or to defend one of the standard positions in a novel way. Still less do I pretend to offer a comprehensive survey of such positions and how they stand up in light of the latest developments in physics. My excuse is, rather, that I hope to address an entirely different set of philosophical problems. The problems I have in mind certainly have deep connections with the problems of absolute and relative space, time, and motion, and the roles that they play, or might play, in the history and future of physics. But they can't be glossed by the standard questions on space-time metaphysics: is motion absolute or relative? Are space and time substantival or relational? Rather, they are problems concerning how any knowledge of space, time, and motion – or spatio-temporal relations – is possible in the first place. How do we come to identify aspects of our physical knowledge as knowledge of space and time? How do we come to understand features of our experience as indicating spatio-temporal relations? How do the laws of physics reveal something to us about the nature of space and time?