This volume is the proceedings of the IAU Symposium "Star Clusters." It includes the invited papers, brief accounts of the contributed papers, and the associated discussion. The topics discussed at the symposium included many aspects of recent research on open clusters and globular clusters. Because cluster studies touch on so many areas of stellar, galactic and extragalactic astronomy, this volume should be of interest to a wide astronomical readership. In setting up the scientific program for this symposium, the scientific organizers were mindful of a very successful NATO Advanced Study Institute at Cambridge (UK) in August, 1978, at which recent advances in globular cluster studies were thoroughly reviewed. So the emphasis at this symposium was on open clusters and problems common to open and globular clusters. One day only was scheduled exclusively for globular clusters, and the topics chosen for that day are ones in which rapid progress is being made. We would like to mention here two aspects of this symposium which contributed significantly to the useful and relaxed discussion following the scientific contributions.