|In participants' narratives, observers' accounts, and scholarly analyses of U.S. counterhegemonic social movements, one frequently encounters the term 'faith' in characterizations of participants' engagement with a movement and its goals. In such references, people use the term 'faith' and related terms to signal that participants engage with the movement in a manner that is traditionally associated with religion and religious faith (even when a movement is overtly secular in orientation); that is, participants give themselves over to the cause with which they are involved. Using 'faith' as a starting point, I address the following questions: What is the nature of participants' engagement in a counterhegemonic social movement? How is that engagement perceived and confronted by outside observers? How do this engagement and perceptions of it influence the dynamics within counterhegemonic social movements? In order to answer these questions, I examine three U.S. social movements between 1890 and 1940. The first case surveys news coverage of the 1890 Lakota Ghost Dance, focusing on outsiders' perceptions of Ghost Dance faith, examining charges of delusion and fanaticism, and considering the ways in which these perceptions affected responses to the movement. The second case tracks messianism in three books by W. E. B. Du Bois in order to understand his attempts to theorize the nature and role of faith in the cause of racial liberation. The third case explores the dynamics of 1930s U.S. communism by investigating participants' own understandings of the category of 'faith,' as well as examining critics' and historians' analyses of the movement, given their own use of the term 'faith.' Based on these case studies, I argue that taking a collective counterhegemonic stand in order to achieve substantive social change often involves a quality of engagement that: opens one up to charges of delusion and fanaticism; requires conscious and self-critical cultivation on the part of participants and leaders; and treads a find line between prophetic vision and dogmatic blindness. Throughout this dissertation, I demonstrate the centrality of this kind of engagement---this phenomenon of 'giving oneself over to a cause'---in the dynamics of counterhegemonic social movements.