This book has remained one of the most popular representations of the theory of relativity to this day. In the present version, J. Ehlers and M. Pössel from the Max Planck Institute for Gravitational Physics have commented on Born's text and added an extensive supplementary chapter that preserves Born's vivid yet precise style while tracing the tumultuous development of the theory of relativity up to our present day. It addresses gravitational waves and black holes, recent developments in cosmology, approaches to a theory of quantum gravity, and the numerous sophisticated experiments that have increasingly confirmed the validity of Einstein's theory. Thus, this book continues to be one of the most immediate accesses to the theory of relativity for anyone interested in the subject.