Most of the available evidence suggests that there is a positive correlation between social media use and engagement in collective action, such as social movements and political protests. However, we do not know if this correlation results from a causal effect or, instead, merely reflects that participants happen to use social media more often. So long as the potential mechanisms by which online social networks may lead people to engage in collective action remain obscure, any causal attribution remains suspect. Furthermore, we know little about the communication flows that transpire in social media, including the conditions under which using Twitter, Facebook and similar platforms may influence citizens’ political behavior. Using a variety of quantitative and qualitative methods—including human and automated content analysis, cross-sectional and panel surveys, social network analysis, “small” and “big” data—I will present some of the work I’ve done mapping the functions, mechanisms and conditions under which social media relates to collective action in Chile.