The 1972 Banff lectures attempted a systematic exposition of the ideas underlying recent developments in general relativity and its astronomical applications at a level accessible and useful to graduate students having some previous acquaintance with the subject. To our regret, it was not possible to include any printed record of Peebles' beautiful lectures on observational cosmology or of the many stimulating seminars on special topics contributed by the participants. What remains is nevertheless a reason ably self-contained and compact introduction to Einstein's theory in its modern in carnation, and we hope it will be found useful by the many physicists, astronomers, and mathematicians who wish to update and deepen their understanding of the theory. On behalf of the organizing committee, I should like to express appreciation to a number of people whose help was crucial to the success of the enterprise: to Jan van Kranendonk, who initiated the idea of a Banff summer school on general relativity; to him and to David Rowe and Don Betts for inspiration and moral support; to our indefatigable secretaries Olwyn Buckland and Leslie Hughes; and to Garry Nash, Richard Sigal, Tim Spanos, and Gordon Wilson who helped in a variety of ways to keep the wheels running. How much we owe to the splendid cooperative effort of the lecturers will be clear to any reader of the following pages.

To commemorate the 300th anniversary of the publication of Isaac Newton's Philosophiae Naturalis Principia Mathematica, Stephen Hawking and Werner Israel have assembled a series of unique review papers by many of the world's foremost researchers in cosmology, relativity and particle physics. The resulting volume reflects the significant and exciting advances that have been made in these fields since the editor's acclaimed volume published in 1979: General Relativity: An Einstein Centenary Survey. Newton's immense contribution to the physical sciences is assessed, and its relevance to today's physics made clear. The international contributors then chart the major developments in the study of gravitation, from Newtonian gravity to black hole physics. In the fields of galaxy formation, inflationary and quantum cosmology, and superstring unification, the book provides important overviews written by workers involved in many of the advances described. By shaping such a wide-ranging and scholarly series of articles into a cohesive whole, the editors have created a fitting and lasting memorial to the man who continues to inspire scientists the world over. This book is an essential reference source of the latest advances in gravitational physics and relativistic cosmology.