The lAU Colloquium No. 56, the Second lAU Colloquium, On Reference Coordinate Systems for Earth Dynamics, co-sponsored by the COSPAR and the International Association of Geodesy of IUGG was held in Warsaw, Po1and, on September 8-12, 1980. The Co11oquium was organized by the Space Research Centre of the Po1ish Academy of Sciences and the Smithsonian Institution Astrophysica1 Observatory. It was sponsored by the Committee of Astronomy, the Committee of Geodesy, and the Committee of Space Research of the Po1ish Academy of Sciences. The first Co11oquium devoted to this subject was held in Torun, Po1and, in 1974. The Scientific Organizing Committee consisted of: Cochairmen Dr. E. M. Gaposchkin USA Dr. B. Ko~aczek Po1and Members of the Program Committee Prof. J. Kova1evsky France Prof. I. I. Mueller USA Prof. M. Rochester Canada Members Dr. M. Bursa Czechos1ovakia Dr. H. K. Eichhorn USA Prof. W. Fri cke FRG Dr. E. Hog Denmark Dr. Y. Kozai Japan Dr. Y. S. Yatskiv USSR The Loca1 Organizing Committee consisted of: Dr. B. Ko~aczek, Chairman Dr. W. Pache1ski, Secretary Dr. W. Dobaczewska Dr. J. Krynski Dr. G. Sitarski Prof. J. Smak Dr. J. B. Zielinski Mr. W. Zarnowiecki ix E. M. Gaposchkin and B. Kotaczek (eds. ), Reference Coordinate Systems for Earth Dynamies, ix-x. Copyright (c) 1981 by D. Reidel Publishing Company. x PREFACE The duties of chairmen of the sessions were performed by Dr. J. Zielinski, Dr. P. Bender, Prof. W. Fricke, Dr. B.