This book is written to give first year undergraduates a comprehensive understanding of the theory of special relativity. It cannot do that using only the mathematics that first year undergraduates accumulate before their second year, and so the necessary extra mathematics is included in the book. This makes the book more than just a book on the theory of special relativity. The book is also an introduction to some of the mathematics that students will meet in the later years of their studies.This book concentrates on presenting the theory of special relativity as the geometry of space-time. The presentation is straightforward, complete and reader-friendly, with explanatory asides, which give historical context and links with other branches of physics and mathematics. The first four chapters give a complete description of the special theory and the nature of space and time, with the minimum use of mathematics. The mathematics necessary is introduced in the following five chapters, with the final fifteen chapters devoted to a comprehensive and detailed exposition of Einstein's special relativity.