Situated in the gap between electronics and optics, the terahertz frequency range of the electromagnetic spectrum has long been of interest to only a limited number of scientists and engineers due to a lack of efficient and affordable terahertz sources and detectors. But the advent of femtosecond lasers in the 1980s and photoconductive switches in 1084 have made the terahertz gap accessible, while at the same tune advances in electronics and optics have made it narrower. Research activities in terahertz frequencies have risen dramatically since that time and funding has increased remarkably in the last decade. In spite of the enormous recent interest in the terahertz range, there are as yet very few books describing selected efforts in this field. In particular. Japanese work has not been published coherently at all, although much of the progress in the terahertz field originates from this country. In this book we will present recent and important developments in the field of terahertz radiation with emphasis on terahertz pulse radiation and on work carried out in Ларап.