This systematic approach to the quantum theory of collective phenomena is based principally on the model of infinite systems. Suitable for advanced undergraduates and graduate students of physics and chemistry, the three-part treatment begins with an exposition of the generalized form of quantum theory of both finite and infinite systems. Part II consists of a general formulation of statistical thermodynamics, and the final part provides a treatment of the phenomena of phase transitions, metastability, and the generation of ordered structures far from equilibrium. ""An excellent and competent introduction to the field ... [and] ... a source of information for the expert."" - Physics Today""This a book of major importance.... I trust that this book will be used as a basis for the teaching of a balanced, modern and rigorous course on statistical mechanics in all universities."" - Bulletin of the London Mathematical Society""This is one of the best introductions to the subject, and it is strongly recommended to anyone interested in collective phenomena."" - Physics Bulletin ""The book may be recommended for students as a well-balanced introduction to this rich subject and it can serve as a useful handbook for the expert."" - Journal of Statistical Physics