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 one does the work and the common interest is t realised. This book analyses the social pressure whereby groups solve the problem of collective action. The authors break new ground in showing that the problem of collective action requires a model of group process and cant be deduced from simple models of individual behaviour. They employ formal mathematical models to emphasise 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, ecomists, 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.