It is the aim of this book to describe in concise form our present theoretical understanding of the nuclear many-body problem. The presen- tation of the enormous amount of material that has accumulated in this field over the last few decades may be divided into two broad categories: One can either concentrate on the physical phenomena, such as the single-particle excitations, rotations, vibrations, or large-amplitude collec- tive motion, and treat each of them using a variety of theoretical methods; or one may stress the methodology and technical aspects of the different theories that have...