The new edition of the second volume of Cohen-Tannoudji's groundbreaking textbook introduces concepts such as the quantum theory of scattering by a potential, special and general cases of adding angular momenta, time-independent and time-dependent perturbation theory, and systems of identical particles. The entire book has been completely revised to take into account new developments in quantum mechanics curricula. The textbook retains the typical Cohen-Tannoudji style also in the new edition: it explains the fundamental concepts in chapters which are elaborated in accompanying complements that provide more detailed discussions, examples and applications.