The analysis and theorization of social movements is central to understanding social life, state-society relations, and social change, and comprises one of the most vibrant areas of sociological research today. Theories of collective action and mobilization typically aim to understand the factors and conditions producing organized collective action dedicated to fostering or resisting change across time and place, as well as the consequences of those challenges. In light of our conceptualization of social movements as collectivities that seek to challenge or defend existing institutional and/or cultural systems of authority and their associated practices, we provide an overview of dominant paradigms used to conceptualize and theorize the emergence, dynamics, and outcomes of social movements. We then conclude by drawing on recent innovations in the field to suggest ways that scholars can refine, elaborate, and expand the existing theoretical repertoire.