Neutrinos play a decisive part in nuclear and elementary particle physics, as well as in astrophysics and cosmology. Some of their most basic properties, such as their mass and charge conjugation symmetry, are largely unknown. This book focuses on what we know and may hope to know about the mass of the neutrino and its particle-antiparticle symmetry. Topics include neutrino mixing, neutrino decay, neutrino oscillations, double beta decay, solar neutrinos, supernova neutrinos and related issues. The authors stress the physical concepts, and discuss both theoretical and experimental techniques. This updated second edition differs from the first in that it contains an expanded coverage of experimental results and theoretical advances. Since publication of the first edition, many issues that were at that time unresolved, such as tritium beta decay and reactor neutrino oscillations, have been clarified and are discussed here. Also included is an expanded coverage of solar and supernova neutrinos. This book deals with one of the most intriguing issues in modern physics, and will be of value to researchers, graduate students and advanced undergraduates specializing in experimental and theoretical particle physics and nuclear physics.