This volume contains all but one of the lectures and seminars presented at the NATO Advanced Study Institute on HOI Thin Plasmas in Astrophysics held in Cargese, Corsica, from September 8 to 18, 1987. The meeting was planned in collaboration with the members of the Scientific Organizing Committee, 10 whom I am grateful for suggesting a comprehensive and well balanced program. The SOC was comprised of Prof. J. Bleeker (Space Research Institute. Utrecht, The Netherlands), Dr. C. Cesarsky (CEN Saclay, France), Dr. R. Mushotzky (GSFC, USA), Prof. K. Pounds (University of Leicester, UK), Prof. H. Schnopper (Danish Space Research Laboratory, Denmark), Dr. H. Tananbaum (Center for Astrophysics, USA), Dr. G. Trinchieri (Arcetri Observatory, Italy), and Prof. 1. Truemper (MPE, Garching, Germany). The ASI, fully supported by the NATO Scientific Affairs Division, was organized with the intent of providing a critical and up-to-date overview of our present kowledge and understanding of the properties of hot thin plasmas in astrophysics as they are revealed by X-ray observations from space. The X-ray and UV emission from optically thin thermal plasmas is a common feature of many astrophysical systems. This type of emission occurs in the solar corona and in the coronae of other stars, in supernova remnants and in the hot interstellar medium, in normal galaxies and galactic halos, and in the intergalactic gas in clusters.