The wave of sit-ins that swept through the American South in the spring of 1960 transformed the struggle for racial equality. This episode is widely cited in the literature on social movements, but the debate over its explanation remains unresolved—partly because previous research has relied on case studies of a few large cities. The authors use event-history analysis to trace the diffusion of sit-ins throughout the South and to compare cities where sit-ins occurred with the majority of cities where they did not. They assess the relative importance of three channels of diffusion: movement organizations, social networks, and news media. The authors find that movement organizations played an important role in orchestrating protest; what mattered was a cadre of activists rather than mass membership. There is little evidence that social networks acted as a channel for diffusion among cities. By contrast, news media were crucial for conveying information about protests elsewhere. In addition, the authors demonstrate that sit-ins were most likely to occur where there were many college students, where adults in the black community had greater resources and autonomy, and where political opportunities were more favorable.