Thoroughly revised and updated, and now also including special relativity, this book provides a pedagogical introduction to relativity. It is based on lectures given by the author in Jena over the last decades, and covers the material usually presented in a three-term course on the subject. It is self-contained, but the reader is expected to have a basic knowledge of theoretical mechanics and electrodynamics. The necessary mathematical tools (tensor calculus, Riemannian geometry) are provided. It covers the most important feature of both special and general relativity, as well as touching on more difficult topics such as the field of charged pole-dipole particles, the Petrov classification, groups of motion, exact solutions and the structure of infinity. The book is written as a textbook for undergraduate and introductory graduate courses, but will also be useful as a reference for practicing physicists, astrophysicists and mathematicians. Most of the mathematical derivations are given in full and exercises are included where appropriate. The bibliography gives many original papers and directs the reader to useful monographs and review papers.