The long list of “spin glass materials” and the summary of the experimental results provided in this book emphasize the common features of spin glasses despite the diversities. The critical review of more than a thousand papers not only identifies the complexities involved in the theoretical understanding of the static and dynamic properties of real spin glasses but also explains the physical concepts and mathematical formalism which have been used so successfully in solving the infinite range model. Morever, a beginner will find practical applications of the concepts of broken ergodicity, ultrametricity, gauge invariance, etc. in this book. Major progress has been made in solving many other challenging problems, e.g., computer design, associative memory, pattern recognition and neural networks, evolution of biological species etc. by mapping them onto the spin glass models. The chapter on these spin- glass-like systems will be useful not only to physicists but also to computer scientists and biologists.