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.