This book provides course material in theoretical physics intended for undergraduate and graduate students specializing in condensed matter. The book derives from teaching activity, offering readable and mathematical treatments explained in sufficient detail to be followed easily. The main emphasis is always on the physical meaning and applicability of the results. Many examples are provided for illustration; these also serve as worked problems.
Discussion extends to atomic physics, relativistic quantum mechanics, elementary QED, electron spectroscopy, nonlinear optics, and various aspects of the many-body problem. Methods such as group representation theory, Green¿s functions, the Keldysh formalism and recursion techniques were also imparted.

I-Introductory Many-Body Physics.- Basic Many-Body Quantum Mechanics.- Adiabatic Switching and Time-Ordered series.- Atomic Shells and Multiplets.- Green¿s Functions as Thought Experiments.- Hopping Electron Models: an Appetizer.- Many-body Effects in Electron Spectroscopies.- Symmetry in Quantum Physics.- Group Representations for Physicists.- Simpler Uses of Group Theory.- Product of Representations and Further Physical Applications.- More on Green Function Techniques.- Equations of Motion and Further Developments.- Feynman Diagrams for Condensed Matter Physics.- Many-Body Effects and Further Theory.- Non-Equilibrium Theory.- Non-Perturbative Approaches and Applications.- Some Recursion Techniques with Applications.- Aspects of Nonlinear Optics and Many-Photon Effects.- Selected Exact Results in Many-Body Problems.- Quantum Phases.- Pairing from repulsive interactions.- Algebraic Methods.- Appendices.- Appendix 1: Zero-point Energy in a Pillbox.- Appendix II-Character Tables.- Proof of the Wigner-Eckart Theorem.

Professor Michele Cini is a full professor of solid state theory at the Department of Physics , University of Roma Tor Vergata. Born in Pisa (Italy) in 1946, he graduated there in 1969. He is the author of about 100 theoretical research papers dealing with electron spectroscopies, nonlinear optics, recursion methods, electronic transport, antiferromagnetism and superconductivity.