Fully indexed, the 1991 edition of the Yearbook is the single most current, comprehensive and authoritative reference publication about the work of the United Nations, other international organizations and related bodies. The book is designed not just for use by diplomats, officials and scholars but also by other researchers, writers, journalists, teachers and students. The year 1991 was a remarkably eventful one for the United Nations and in the conduct of international relations. This volume of the Yearbook details the activities of the United Nations, its many organs, agencies and programmes, working together to rekindle a new form of multilateral cooperation for a better world. It records the diverse and globe-encompassing activities of the United Nations and its enduring efforts to deal with the world's pressing concerns, particularly matters of international peace and security, disarmament, human rights, the settlement of regional conflicts, economic and social development, the preservation of the environment, control of drugs and narcotic substance abuse, crime prevention, adequate shelter, youth and the ageing and humanitarian assistance for refugees as well as disaster relief. The Yearbook of the United Nations is now up-to-date. The Yearbooks for the years 1988, 1989 and 1990 will be published simultaneously.

The XXth General Assembly of the International Astronomical Union was held in Baltimore, Maryland USA from August 02 to 11, 1988. The Inaugural Ceremony on August 02 was held in the presence of representatives of the United States Governn:ent, t~e S~ate of Maryland, the City of Baltimore and the host institution -the Johns Hopkins Umverslty- as well as of the National and Local Organising Committees. The scientific programme maintained the high standards of the Union and the scientific proceedings may be found either in this volume or in volume 8 of Highlights of Astronomy. The scientific programme was organised by the 40 Commission Presidents and coordinated by the General Secretary (1985-1988), Dr. J.-P. Swings. The local arrangements were effectively made through the National Organising Committee under the Chairmanship of Prof. F. Drake and the Local Organising Committee under the co-Chairmanship of Prof. A. Oavidsen and Dr. R. Giacconi. The smooth day to day operation of the meeting resulted from the incomparable dedication of Karen Weinstock and Harold Screen.