This book is the result of a meeting held in August, 1986 in Irsee, West Germany. As the title suggests, the aim of the meeting was to discuss physical processes in interstellar clouds, determine the current status, aims and future direction of the research in this area. Interstellar clouds contain nearly all the mass of diffuse gas in our galaxy, some 10% of the total galactic mass. They represent the birth site for stars and the final "dumping ground" for matter ejected from stars (winds, ex plosive ejecta) and thus play an integral part in the galactic recycling of material. Not only are the clouds important for the structure and evolution of our galaxy, they are also interesting objects of study "per se." Because of their vast scales (up to about 100 parsec), extreme temperatures (as low as about lOOK), and long life 8 times (estimated a about 10 years) a number of physical and chemical processes occur in these environments, which we are not able to study elesewhere, certainly not in laboratories. It is for this reason that the meeting, and hence this book, was organized in such a way that firstly the latest observational results were sum m ized, going from the global, large scales, to finer details and dynamics, then progressing onwards to the processes -dynamical, chemical, electromagnetic, etc."

This book contains the invited and contributed lectures presented at a meeting organised in the context of the XVIII general assembly ofthe IAU, held in Patras, August 19, 1982. Roughly one hundred scientists attended this meeting, the discussions were livel- sometimes heated - and the original time span allocated to the meeting was as a result, comfortably exceeded by about 50 % . The aim of this meeting was to determine the role of galactic gamma-ray astronomy within the general concept of galactic astrophysics. The timing, at the end of the COS-B mission, was regarded as opportune, because it gives interested astrophysicists the possibility for interdisciplinary studies using the existing gamma-ray data base (e.g. comparison with infrared, radio, X-ray, etc. astronomies), as well as for theoretical studies. The next generation of gamma-ray detectors will probably not be in operation for another 5 to 10 years, and therefore it is hoped that the proceeding of this meeting can be used (in the intermediate time) as a basis for further studies, as a stimulation for more theoretical work and as an important contribution for defining the aims and operation of future gamma-ray missions. The interrelationship with other branches of astronomy, the astrophysical implications and the study of relevant physical processes using available measurements in the near-Earth environment were important results of the meeting. Many persons contributed to the success of the meeting, in particular all those who either presented a contribution and/or took part in the discussions.

This book is the result of a meeting held in August, 1986 in Irsee, West Germany. As the title suggests, the aim of the meeting was to discuss physical processes in interstellar clouds, determine the current status, aims and future direction of the research in this area. Interstellar clouds contain nearly all the mass of diffuse gas in our galaxy, some 10% of the total galactic mass. They represent the birth site for stars and the final "dumping ground" for matter ejected from stars (winds, ex plosive ejecta) and thus play an integral part in the galactic recycling of material. Not only are the clouds important for the structure and evolution of our galaxy, they are also interesting objects of study "per se." Because of their vast scales (up to about 100 parsec), extreme temperatures (as low as about lOOK), and long life 8 times (estimated a about 10 years) a number of physical and chemical processes occur in these environments, which we are not able to study elesewhere, certainly not in laboratories. It is for this reason that the meeting, and hence this book, was organized in such a way that firstly the latest observational results were sum m ized, going from the global, large scales, to finer details and dynamics, then progressing onwards to the processes -dynamical, chemical, electromagnetic, etc."