When this book was originally published in 1979, the vitality of Einstein's general theory and its impact on other branches of science had never been greater. The unprecedented advances of the previous fifteen years had been stimulated on the observational side by developments in radar and space technology and by the discovery of exotic astronomical objects, which pointed to the existence of very strong gravitational fields, and possibly black holes, in many parts of the universe. Equally striking had been the progress in theoretical understanding, notably of black hole physics, the early history of the universe and the reconciliation of quantum physics and gravitational theory. To honour Einstein's hundredth birthday, twenty-one of the world's leading relativists collaborated on this carefully integrated survey of the state of research. This unique book, which remained a standard for many years, is indispensable to anyone concerned with the profound influence that Einstein's theory has exerted on our notions of space, time and the ultimate nature of matter.