Sociologists have often defined social movement activity against other, more institutional forms of political engagement, including activism in political parties. This dissertation attempts to develop a more flexible, organic and systemic understanding of the relationship between movements and parties by examining the impact of social movements on the California Democratic Party (CDP). The research is based in participant observation of the Party's activity at all levels, data from a 2011 survey of 524 CDP convention delegates (out of a total of 2556), as well as interviews with current and past CDP leaders, activists and staff. The findings are contextualized in a broad, historical narrative of structural and cultural change surrounding the Democratic Party nationally. Despite the theoretical division between movements and parties, this study finds significant overlap between these two forms of political activity.

Individual activists transition relatively freely between "movement activism" and "party activism" in order to achieve their larger goals. Political parties are also shaped by the activity of social movement groups and organizations within their structures. Recent changes in the style and organization of political campaigns have produced further convergences between movement and party organizations. This has been the case in California, where several waves of movement and grassroots activists have successfully pushed for greater participatory opportunities within the Party and stronger commitments to core values. Surprisingly, the data suggest that movement activity in the CDP may have helped to strengthen the Party's ability to better fulfil its traditional political functions, despite the well-documented hostility to party prerogatives that characterize California's political culture and electoral system.

In a context in which party organizations' role in politics is heavily circumscribed, CDP leaders and activists have created an organization that is both effective electorally as well as comparatively independent and participatory. That social movements and movement activists have played a role in the narrative of conflict and cooperation that produced this outcome is significant---both for scholars interested in the impact of movements on institutional politics, as well as students of political parties interested in preserving or expanding the crucial role they play in modern democracies.