The problem of collective action is that each member of a group wants other members to make necessary sacrifices while he or she 'free rides', reaping the benefits of collective action without doing the work. Inevitably the end result is that no one does the work and the common interest is not realized. This book analyses the social pressure whereby groups solve the problem of collective action. The authors show that the problem of collective action requires a model of group process and cannot be deduced from simple models of individual behaviour. They employ formal mathematical models to emphasize the role of small subgroups of especially motivated individuals who form the 'critical mass' that sets collective action in motion. The book will be read with special interest by sociologists, social psychologists, economists and political scientists. It will also be of concern to those in industrial relations and communications research working on issues in collective action and rational choice.