This book aims to provide a survey of the current state of research in the physics of neutrinos, which has undergone dramatic development during the last decade, in a form accessible to the nonspecialist and the graduate stu dent. The major issue during the last two decades has been the neutrino mass, whereas the interaction of neutrinos was well understood within the framework of the standard theory, which was established in the 1970s. In 1994, we published a textbook-format review article "Physics 01Neutrinos' in "Physics and Astrophysics 01 Neutrinos," in anticipation that the mass of the...