This book presents the history of space-time physics, from Newton to Einstein, as a philosophical development re?ecting our increasing understanding of the connections between ideas of space and time and our physical knowledge. It suggests that philosophy’s greatest impact on physics has come about, less by the in?uence of philosophical hypotheses, than by the philosophical analysis of concepts of space, time, and motion and the roles they play in our assumptions about physical objects and physical measurements. This way of thinking leads to new interpretations of the work of Newton and Einstein and the connections between them. It also offers new ways of looking at old questions about a-priori knowledge, the physical interpretation of mathematics, and the nature of conceptual change. Understanding Space-Time will interest readers in philosophy, history and philosophy of science, and physics, as well as readers interested in the relations between physics and philosophy.