This book contains the papers presented at the "First International Sympo st sium on Aerogels (1 ISA)", held in September 1985 at. the University of Wiirzburg, Fed. Rep. of Germany. It was the first meet.ing of this kind, wit.h participants from several European count.ries, the United States of America, Canada, South America, and Africa. The meeting was interdisciplinary, with most of the participants being physicists, chemists or material scientists ei ther from universities or from industrial research institutes. Let me try to shed some light upon the class of substances the symposium was about: Aerogels are extremely porous high-tech materials, consisting ei ther of silica, alumina, zirconia, stannic or tungsten oxide or mixtures of these oxides. Due to their high porosity (up t.o 99%!) and t.heir large inner surface, aerogels serve as especially active catalysts or as catalytic subst.rates, as adsorbents, fillers, reinforcement agents, pigments and gellifying agents. Silica aerogels as translucent or transparent superinsulating fillers in window systems could help to considerably reduce thermal losses in windows and to improve the energy balance in passive solar systems. Aerogels also have fas cinating acoustic properties - the sound velocity can be as low as 100 m/s! The production of aerogels starts with the controlled conversion of a sol into a gel: The growth of clusters or polymer chains from a chemical solution, the cross-linking of these primary entities and the formation of a coherent network - still embedded in a liquid.