Social movements have a long tradition as agents of social change. In recent years, they have regained significant public visibility, as seen with the Arab Spring, Occupy Wall Street, or Pegida. Social sciences have been concerned with the question of under what circumstances social movements arise and succeed since their inception. This volume provides an overview of theories about social movements, offering a conceptual toolbox to capture, describe, and explain current phenomena. Its comparative theoretical perspective allows for the observation and understanding of not only social movements themselves but also their conceptualization in the social sciences over time.