Stephen Hawking, the Lucasian Professor of Mathematics at Cambridge University, is widely regarded as one of the most brilliant theoretical physicists of our time. This book contains a personal selection of his most significant papers on gravitational theory applied to cosmology and black holes. His early work, partly in collaboration with Roger Penrose, showed that spacetime must come to an end at singularities that will occur both in the big bang and in black holes. This means that time will have a beginning and an end. Hawking's later work has been concerned with understanding these two situations. This requires a combination of the two great theories of the first half of the 20th century: general relativity and quantum mechanics. Although a completely unified theory remains elusive, Hawking has been able to make considerable progress, both with black hole radiation and with the no-boundary proposal for the origin to the universe. This compilation of Stephen Hawking's most important works, complete with an introduction by him, is an essential collector's item and an important source of reference for theoretical physicists. It bears testimony to the courage of a man who has overcome severe physical disability to push the frontiers of science to new heights.