This volume is a collection of the scientific papers of Frederick Reines. Its publication is to commemorate the 70th birthday, in 1988, of this distinguished scientist. The selected papers here cover many aspects of his work in neutrino physics, astrophysics and conservation law tests. They have been divided into logical groupings, each introduced by a leading authority in that field, who helps the reader to see the reprinted articles with a better historical and scientific perspective.