On January 20-21, 1964, the Institute for Space Studies of the Goddard Space Flight Center, National Aeronautics and Space Administration, was host to an international group of astronomers, physicists, and Earth scientists, gathered to discuss the Earth-Moon system. This was the sixth in a continuing series of interdisciplinary meetings on topics in space physics held at the Institute. The conference was organ ized by G.J.F. MacDonald, of the University of California at Los Angeles, and by R.H. Dicke, of Princeton University. The working title of the conference was "The Dynamics of the Earth-Moon System," and indeed much of the contents of this proceedings volume is concerned with dynamical problems, but the conference dealt with many other topics concerning the Earth-Moon system, and hence we have adopted the shorter title for this volume. The conference proceedings have been somewhat rear.. ranged from the order in which the papers were actually presented. In doing this the editors are exercising hindsight to bring together closely related discussions. The first paper, by D. Brouwer, discusses the motions and moments of inertia of the Moon and their relation to the lunar figure and composition. From this discussion it emerges there remain many uncertainties in the motion of the Moon associated with the lunar composition and the distribution of its mass."

The many papers by Soviet authors have been translated into English by A. P. Kirillov, N. A. Nikiforova, E. A. Voronov, and others. Some of the papers were trans lated by the authors themselves. The discussion records have been prepared at the Institute for Theoretical Astronomy by V. K. Abalakin, N. A. Belyaev, A. P. Kirillov, V. A. Shor, E. A. Voronov, N. S. Yakhontova, and others. The three papers published in French have been carefully checked by B. Milet. The final editing has been done at the Smithsonian Astrophysical Observatory, and we thank J. H. Clark, P. D. Gregory, J. E. Kervick, and G. Warren for retyping much of the material. Our special thanks are due to the D. Reidel Publishing Company for the excellent care they have taken in printing these proceedings of IAU Symposium No. 45. G. A. CHEBOT AREV E. I. KAZIMIRCHAK-POLONSKA Y A B. G. MARSDEN INTRODUCTION The idea to organize a Symposium on 'The Motion, Evolution of Orbits, and Origin of Comets' dates back to the IAU thirteenth General Assembly, held in 1967 in Prague. Owing to the impossibility of completing during the General Assembly the discussion on the problem of orbital evolution of comets Professor G. A. Chebotarev, then the newly elected President of IAU Commission 20, initiated the organization of the international symposium in Leningrad where the full scope of cometary problems might be considered from the viewpoint of celestial mechanics."