I Inaugural Ceremony.- Address by Dr. A. Davidsen, co-Chairman of the Local Organizing Committee.- Address by Dr. R. Giacconi, co-Chairman of the Local Organizing Committee.- Address by Dr. F. Drake, Chairman of the National Organizing Committee.- Address by Dr. S. Muller, President of the Johns Hopkins University.- Address by K.L. Schmoke, Mayor of the City of Baltimore.- Address by M.A. Steinberg, Lieutenant Governor of the State of Maryland.- Address by Dr. F. Drake, on behalf of Dr. B. Shakhashiri, Assistant Director for Science & Engineering Education, National Science Foundation.- Address by Dr. N.W. Hinners, Associate Deputy Administrator, NASA Headquarters.- Address by Dr. W. R. Graham, Science Advisor to the President & Director of the Office of Science & Technology Policy.- Address by Prof. J. Sahade, President of the International Astronomical Union.- II Extraordinary General Assembly.- 1. Extension of the membership of the Executive Committee by a President-Elect.- 2. Establishment of a new category of adherence to the Union, Associate National Member.- III Twentieth General Assembly.- Session 1: 2 August, 1988.- 1. Formal opening by the President.- 2. Appointment of Official Interpreters.- 3. Report of the Executive Committee, 1985-1987.- 4. Report of the General Secretary January-August 1988.- nominations for IAU Membership.- report by the General Secretary.- 5. Report by the President on the work of the Special Nominating Committee 1985-1988.- 6. Announcement of.- the names of Official Representatives of Adhering Organizations.- the names of Representatives to serve on the Nominating Committee.- the names of Acting Presidents of Commissions.- 7. Appointment of the Finance Committee.- 8. Appointment of the Resolutions Committee.- 9. Revisions of the Statutes & By-Laws.- 10. Resolutions submitted by Adhering Bodies.- 11. Resolutions submitted by Commissions or by associated Inter-Union Commissions.- Session 2: 11 August, 1988.- 12. Financial matters.- report of the Finance Committee.- votes on proposed budgets for 1988 & 1989-1991.- 13. Financial Resolutions of the Executive Committee.- 14. Resolutions submitted by the Executive Committee.- Amateur-Professional Cooperation in Astronomy.- Coopération entre les astronomes amateurs & professionnels en astronomie.- Adverse Environmental Impacts on Astronomy.- Impacts sur l'environnement nuisibles pour l'Astronomie.- Improvement of Publications.- Amélioration des Publications.- International Space Year 1992.- Année Internationale de l'Espace 1992.- Cooperation to Save Hydroxyl Bands.- Coopération pour la sauvegarde des bandes de OH.- Sharing Hydroxyl Band with Land Mobile Satellite Services.- Partage de la bande Hydroxyle avec les services mobiles au sol.- Revision of Frequency Bands for Astrophysically Significant Lines.- Révision des bandes de frequencies pour les raies d'intérêt astrophysique.- 15. Resolutions submitted by the Resolutions Committee.- Extensions to FITS.- Extensions à FITS.- Working Group on FITS.- Groupe de travail sur FITS.- Endorsement of Commission Resolutions.- Soutien des Résolutions des Commissions.- 16. Resolutions submitted by Commissions.- WGRF Resolutions.- Résolutions du Groupe de travail sur les repères de références (GWFR).- WGRS -A Continuing Intercommission Project.- Reconduction du WGRS.- Flare 22 Programme.- Programme d'étude des éruptions du cycle 22.- Continuous Survey of Solar Phenomena.- Surveillance continue des phénomènes solaires.- Databases on Minor Planets.- Bases de données sur les petites planètes.- Extension of Global Position Catalogues.- Extension des Catalogues Globaux de Positions.- Availability of the Global Positioning System (GPS).- Disponibilité du GPS.- Need for Accurate Time.- Besoin d'un temps exact.- IAU Contribution to FAGS.- Contribution de l'UAI à FAGS.- Needed History on BIH & IPMS.- Besoin de l'histoire du BIH & de l'IPMS.- 17. Appointment of the Special Nominating Committee.- 18. Nominations of the new Members of the Union.- 19. Applications for IAU Membership.- Application from Algeria.- Application from Iceland.- Application from Malaysia.- Application from Morocco.- Application from Peru.- Application from Saudi Arabia.- 20. Changes in Commissions.- Commission Presidents & Vice-Presidents.- Organizing Committees of Commissions.- 21. IAU Representatives to other Organisations.- 22. Place & date of the XXIth General Assembly.- 23. Election to the Union of a President, a President-Elect, six Vice-Presidents, a General Secretary & an Assistant General Secretary.- 24. Address by the President 1985-1988.- 25. Address by the President 1988-1991.- 26. Closing Ceremonies.- IV Report of the Executive Committee.- Executive Committee 1985-1988.- 1. Introduction.- 2. Administration.- Executive Committee meetings.- Officers' Meetings.- IAU Secretariat.- IAU Staff.- Adhering Countries.- Members of the IAU.- Consultants to IAU Commissions.- 3. Commissions of the IAU.- 4. Scientific Meetings.- Symposia.- Colloquia.- Co-sponsored Meetings.- Regional Meetings.- IAU/UNESCO Young Astronomers' Schools.- XIXth General Assembly, New Delhi, India, 1985.- 5. Publications.- Publisher.- Sales.- Information Bulletin.- 6. Relations to other organisations.- 7. Financial matters.- Summarised accounts.- Comments on summarised accounts.- Balance 1985-1987.- Residual budget 1988.- Adopted budget for 1989-1994.- 8. List of Adhering Organisations.- 9. List of deceased Members.- 10. List of IAU Publications.- Transactions & Highlights.- IAU Symposia volumes.- IAU Colloquia volumes.- Proceedings of Regional Astronomy Meetings.- Miscellaneous Publications.- Commissions' Publications.- V Report of Meetings of Commissions.- 4 Ephemerides (Ephémérides).- 5 Documentation & Astronomical Data (Documentation & données astronomiques).- 6 Astronomical Telegrams (Télégrammes astronomiques).- 7 Celestial Mechanics (Mécanique céleste).- 8 Positional Astronomy (Astronomie de position).- 9 Instruments & Techniques.- 10 Solar Activity (Activité solaire).- 12 Radiation & Structure of the Solar Atmosphere (Radiation & structure de l'atmosphère solaire).- 14 Atomic & Molecular Data (Données atomiques & moléculaires).- 15 Physical Study of Comets, Minor Planets & Meteorites (Etude physique des comètes, des petites planètes & des météorites).- 16 Physical Study of Planets & Satellites (Etude physique des planètes & des satellites).- 19 Rotation of the Earth (Rotation de la Terre).- 20 Positions & Motions of Minor Planets, Comets & Satellites (Postitions & mouvements des petites planètes, des comètes & des satellites).- 21 Light of the Night Sky(Lumière du ciel nocturne).- 22 Meteors & Interplanetary Dust (Météores & poussière interplanétaire).- 24 Photographie Astrometry (Astrométrie photographique).- 25 Stellar Photometry & Polarimetry (Photométrie & polarimétrie stellaire).- 26 Double & Multiple Stars (Etoiles doubles & multiples).- 27 Variable Stars (Etoiles variables).- 28 Galaxies.- 29 Stellar Spectra (Spectres stellaires).- 30 Radial Velocities (Vitesses radiales).- 31 Time (L'heure).- 33 Structure & Dynamics of the Galactic System (Structure & dynamique du système galactique).- 34 Interstellar Matter (Matière interstellaire).- 35 Stellar Constitution (Constitution des étoiles).- 36 Theory of Stellar Atmospheres (Théorie des atmosphères stellaires).- 37 Star Clusters & Associations (Amas stellaires & associations).- 38 Exchange of Astronomers (Echange d'astronomes).- 40 Radio Astronomy Radioastronomie.- 41 History of Astronomy (Histoire de l'astronomie).- 42 Close Binary Stars (Etoiles doubles serrées).- 44 Astronomy from Space (L'astronomie à partir de l'espace).- 45 Stellar Classification (Classification stellaire).- 46 Teaching of Astronomy (Enseignement de l'Astronomie).- 47 Cosmology (Cosmologie).- 48 High Energy Astrophysics (Astrophysique des hautes énergies).- 49 The Interplanetary Plasma & the Heliosphere (Plasma interplanétaire & héliosphère).- 50 Protection of Existing & Potential Observatory Sites (Protection des sites d'observatoires existants & potentiels).- 51 Bioastronomy: Search for Extraterrestrial Life (Bioastromie: recherche de la vie dans l'Univers).- Working Group for Planetary System Nomenclature (Groupe de Travail sur la nomenclature du système planétaire).- VI Functions and Statutes of the Union Pink/FSl.- 1. Useful addresses.- 2. History of the Union.- 3. IAU Representation to other Organisations.- 4. Services of the Union.- 5. Rules for Scientific Meetings.- 6. Statutes, By-Laws & Workings Rules.- Statuts, règlements & directives.- VII Membership Green/Ml.- 1. List of Adhering Countries.- 2. Membership of Commissions.- 3. Geographical Repartition of Members.- within Adhering Countries.- within Non Adhering Countries.- 4. Alphabetical List of Members.- VIII IAU Style Book S1-S50.

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.