The phenomenon of the small world, as in two new acquaintances discovering that they have an acquaintance in common, is of great scientific interest. The samll world phenomenon appears to be a fundamental property of social structure and function. Understanding it, its origin, and its implications can shed light on problems in sociology, sociometrics, political science, social psychology, and anthropology. This volume brings together much of what is understood about the small world problem, and the chapters indicate the quality, vitality, and scope of this area.