Unlike political or economic institutions, social movements have an elusive power, but one that is no less real. From the French and American revolutions through the democratic and workers' movements of the nineteenth century to the totalitarian movements of today, movements exercise a fleeting but powerful influence on politics and society. This study surveys the history of the social movement, puts forward a theory of collective action to explain its surges and declines, and offers an interpretation of the power of movement that emphasises its effects on personal lives, policy reforms and political culture. While covering cultural, organisational and personal sources of movements' power, the book emphasises the rise and fall of social movements as part of political struggle and as the outcome of changes in political opportunity structure.