The central concern of this study is to examine why people choose to join campaigning groups, such as Friends of the Earth or Amnesty, in preference to political parties. Particular emphasis is given, however, to environmental campaign groups. Environmental issues gained increasing political importance in the 1980s, and the environment is mentioned in almost every policy development. There is a high level of public interest in dozens of environmental pressure groups. This study asks: why do people choose to join Friends of the Earth or Amnesty International?; who joins?; how are they targeted?; and why do some leave? Drawing on mainly British and American sources, the authors discuss the significance of the two groups for democracy, and comment on the commitment of the public to campaigning.