Quantum Theory of the Solid State, Part A, describes the concepts and methods, and introduces some of the central problems of the quantum theory of solids. This work is intended to be a single intellectual unit, although for reasons of convenience it has been divided into two parts. Part A contains much of the formalism required for the theoretical study of solids; Part B is oriented toward more specific problems. The present volume includes phenomenological treatments of lattice vibrations and magnetic order; a discussion of symmetry groups; and a description of the properties of one-electron wave functions and the principal techniques for calculating energy levels. Fairly lengthy bibliographies have been included at the end of each chapter to assist readers in making their way through the more specialized periodical literature.This book should be suitable as a textbook for students who have completed a one-year course in quantum mechanics and have some familiarity with the experimental facts of solid state physics. It should also be useful as a reference work.