Dr J. Landi Dessy, Director of the Astronomical Observatory, Cordoba, Argentina, invited the International Astronomical Union to hold a Symposium in Cordoba in connection with the celebration of the Centennial of the Cordoba Observatory; the date of foundation is October 24, 1871. He proposed that the Symposium should deal with Spectral Classification and Multicolour Photometry as seven years had elapsed since the Symposium No. 24 in Saltsj6baden, and much development had occurred in the field. The invitation and the proposal were accepted by the IAU, and the Symposium was held in Villa Carlos Paz, near Cordoba, between October 18 and October 24, 1971. It was attended by about 50 scientists representing Argentina, Canada, Chile, Den mark, France, Germany, Italy, Mexico, Sweden, Switzerland, U.K., U.S.A., Vatican City State and Venezuela. The Symposium was divided into four sessions: 1. Classification of slit spectra, 2. Classification of objective-prism spectra, 3. Photometric classification, 4. Catalogues and documentation. It was decided not to include problems of calibration of absolute magnitudes and temperatures of stars but to refer this to a separate symposium. The contents of the present volume follow closely the programmes of the individual sessions of the Symposium. All the participants at the Symposium appreciated the excellent hospitality of their Argentinian hosts and the efficient help given by the staff ofthe Cordoba Observatory."

The 4th European Regional Meeting in Astronomy, entitled "Stars and Star Systems," was held in Uppsala, Sweden, on August 7 -12, 1978. It was attended by 228 participants from 24 countries. Over 100 papers were presented; this required parallel sessions throughout the Meeting. Financial support was given by the IAU, the Swedish Department of Education, the Swedish Natural Science Research Council, the Swedish Institute and the University of Uppsala. The members of the Scientific and Local Organizing Committees are listed below, and I thank all of them for their contributions to the Meeting. The Meeting was divided into six sections, according to the scien tific topics: Galaxies (A) - including galactic structure and star for mation; High-Energy Astrophysics (B); Stars (C); Interstellar Processes (D); Astronomical Instrumentation (E) and Education in Astronomy (F). In each section a number of Invited Papers were presented as well as a large number of contributed papers. In addition, each day a General Lecture was given by an Invited Speaker. The present volume contains all the General Lectures and all the Invited Papers presented during the Meeting. In three cases, however, and for various reasons, only brief summaries have been available. Abstracts of the contributed papers may be found in Uppsala Astronomical Observatory, Report No. 12."

Proceedings of IAU Symposium No. 50, held in Villa Carlos Paz, Argentina, October 18-24, 1971

In connection with arranging IAU Symposium No. 50 on 'Spectral Classification and Multicolour Photometry', sponsored by Commissions 45 and 25, it was decided to exclude all calibration problems. Instead it was agreed that we should attempt to arrange a separate symposium, dealing with the fundamental problems of the cali bration of absolute magnitudes and temperatures of stars. The Executive Committee of the IAU accepted our proposal, and IAU Symposium No. 54 was held in Geneva on September 12-15, 1972, sponsored by thefollowing IAU Commissions: 24, 25, 29, 33, 35, 37,44 and 45. It was attended by about 90 scientists representing 16 countries. The Symposium was divided into eight sessions. Each session started with a review paper by an invited speaker; this was followed by a general discussion including a few contributed papers. The contents of the present volume follow closely the programmes of the individual sessions of the Symposium. Most of the recorded discussions have been kept, and only in a few cases have the order of questions and comments been altered so as to obtain more homogeneity in the presentation."