In this article, we study protest participants in the May 2006 immigration rights marches in Los Angeles. Analysis of original survey data of 876 march participants yields five main results. First, despite substantial dispute among organizers on how to frame the marches, we find protest participants were similar across march locations organized by different coalitions. Second, we find Spanish-English bilingual participants seemed to benefit from being in two media environments, as they reported more information sources about the protest events than monolingual participants. Third, women reported hearing about the protest events from more information sources, and Spanish-English bilingual women reported hearing from more information sources than any other group, suggesting they acted as social connectors behind the massive participation. Fourth, we confirm the importance of Spanish-language radio as an information source, but our data also point to the significance of television and English-language radio. Finally, analyzing data of first-time protesters, we estimate the immigrant rights marches newly politicized 125,000 people in Los Angeles who spoke Spanish and not English.