This book is intended as an introduction to the philosophical problems of space and time, suitable for any reader who has an interest in the nature of the universe and who has a secondary-school knowledge of physics and mathematics. In particular, it is hoped that the book may find a use in philosophy departments and physics departments within universities and other tertiary institutions. The attempt is always to introduce the problems from a twentieth-century point of view. It is preferable to introduce the history of the topic if and when that history becomes relevant to the development and solution of the problems, rather than to introduce a problem that was of importance in some previous age and to trace the development of it down the years.