Collective action asks a fundamental question in social science: How do sets of actors choose courses of action and work together to achieve desired outcomes, often in opposition to other coalitions? Psychological and economic rationality explanations are incomplete in emphasizing the mental decision processes of individuals. Collective action must be understood at the level analysis of interpersonal and interorganizational relations. Social network theories and methods provide optimal frameworks for explaining collective action in a variety of settings. This book reviews theories and empirical research on collective action in several substantive areas, demonstrates how agent-based models can analyze collective action networks (pandemics, riots, social movements, insurrections, insurgencies), and concludes with speculations about future research directions.