--- - |2 Abstract The notion that mass mobilization has analytically important stages is underappreciated in the literature. This paper proposes an approach that decomposes mass mobilization into three main phenomena: origins, protest and outcome. Each stage is characterized by unique factors and mechanisms. Accordingly, the research questions pertaining to each stage are dealt with by multiple levels of analysis and alternative explanations, allowing theory testing and theory development. The paper highlights separate causal mechanisms that operate in the emergence of grievances and protest motivation during the origins stage; mechanisms involving different forms of pressure, organization, psychological processes, and external forces during the protest stage; and mechanisms pertaining to key players and strategies that determine outcomes of mass mobilization. We illustrate that certain factors and mechanisms which are key in one stage have little or no causal relevance in the other stages. Other factors and mechanisms may also dramatically change in content, meaning or configuration between the stages. This theoretical approach facilitates the integration of a large and diverse body of scholarship into a structured analysis of mass mobilization that allows for both a detailed case study as well as comparison of stages across mass protests. The analysis of stages and causal mechanisms is illustrated across cases of democratization, revolution, and protest within democracy. - Journal for the Theory of Social Behaviour, EarlyView.