A survey of the empirical aspects, the conceptual basis, and the related fundamental problems, as well as the astrophysical and cosmological applications of the title subject. Specific topics include accelerated particle detectors and the operational meaning of the particle concept in curved space-t

Quantum mechanics and quantum field theory on one hand and Gravity as a theory of curved space-time on the other are the two great conc- tual schemes of modern theoretical physics. For many decades they have lived peacefully together for a simple reason: it was a coexistence wi- out much interaction. There has been the family of relativists and the other family of elementary particle physicists and both sides have been convinced that their problems have not very much to do with the problems of the respective other side. This was a situation which could not last forever, because the two...