I found these notes extremely rewarding because not only did they enlarge my physics horizon but they did so where it counts."Physics Today, 1988 "Remarkable clarity and deep physical insight make this book both a valuable tool for theoretical physics students and pleasant reading for researchers in various fields of pure and applied quantum mechanics."Mathematical Reviews, 1987 This book is a collection of lecture notes discussing the basic features of the Quantum Mechanics of Infinite Systems such as collective phenomena, spontaneous symmetry breaking, etc. The mathematical precision has been reduced to a minimum in order to communicate the main ideas to a larger audience including those who are not mathematically meinded. It is aimed at helping students who have difficulty in finding accessible and compact expositions of the material in standard textbooks.