In this book, Sidney Tarrow reviews and synthesizes research on social movements and their dynamics. The book's goal is to offer a theoretical understanding of social movements within the broader universe of contentious politics using historical cases and empirical studies. The first part of the book provides an overview of traditional movements and discusses how social movement theories evolved from structural approaches to resource mobilization and political process theories. This section also examines contained, confrontational, and violent collective actions in movements' contentious repertoire and the state repression and suppression in response to them. The second part mainly discusses organizational aspects of movements: how they are constructed, develop networks, mobilize resources, frame their claims, employ threats and opportunities, and reform their goals, repertoire, and structure across different political regimes. The book's last part uses a 'relational realism' approach and builds on the concepts and theories discussed in the previous sections to explain how the interactions of actors, groups, and institutions lead to different dynamics of contention. Tarrow discusses his 'cycle of contention' concept thoroughly and uses it to describe closed, transformative, and revolutionary movements. This paves the way for discussing how social movements contribute to democratization and democratic recession. A chapter on geographic diffusion of contention follows. Tarrow concludes by arguing that although contemporary challenges, such as radical rightwing movements and high levels of inequality, have established a concerning trend of contentious and violent politics, the social movements discussed in the book suggest that these modern contentions will be transient and institutionalized. The book ends with suggestions for students, scholars, and citizens interested in understanding the dynamics of social movements and their role in modern contentious politics.