The Weak Interaction in Nuclear, Particle and Astrophysics presents concepts of the weak interaction and its integration into modern gauge theories of particle physics, such as grand unification and supersymmetry. The book explores the close connections between micro (nuclear and particle) physics and macro physics (astrophysics and cosmology) induced by the weak interaction. Special attention is given to neutrinos, which have a key role in the understanding of elementary particle theories. In addition to the theoretical aspects, the book covers the important research topics of solar and galactic neutrinos and double beta decay.