The diffusion of networked information and communication technologies has facilitated the rise of novel modes of online collective action, collaboration, and public goods production. In this dissertation, I elaborate an interactional account of online collective action, emphasizing the role of micro-level social interactions in shaping organizational dynamics and collective behavior. This approach provides a clearer explanation of both the means by which individuals and groups within online collectives establish stable patterns of activity as well as the mechanisms through which those patterns change over time. The argument proceeds through a series of interconnected empirical studies of several different domains of online collective action including crowdsourcing labor markets, Wikipedia, and the U.S. political blogosphere. Across these studies, I find that interactions and interactional dimensions of behavior play a central role in mobilizing, retaining, and organizing participants engaged in online collective action. Interactional motives and incentives not only mobilize participation in online collectives, they also contribute to the emergence and persistence of participation patterns and organizational forms. The character of these inequalities and organizational forms vary widely, likely contributing to the uneven impact of online collectives.