The Internet and social media have been considered crucial determinants of recent political turmoil and protests. To estimate the causal impact of Facebook on collective action for a large set of countries, we use its release in a given language as an exogenous source of variation in access to social media where the language is spoken. Using country-, subnational-, and individual-level data, we show that Facebook has had a signi cant and sizable positive impact on citizen protests. Complementary findings show that reverse causality and correlated changes in protest reporting are not driving these results. Facebook's effect is particularly important in countries with: underlying conditions that facilitate using the technology (more Internet access), grievances (economic downturns), few other opportunities to coordinate action against authorities (no freedom of assembly, repression of the opposition), and factors that make the country more confict prone (natural resource abundance, denser urban populations). The effect is also stronger in countries with either very low or very high levels of accountability. Finally, we nd that Facebook impacts individuals with very different characteristics; we detect no evidence of displacement in other forms of political participation or news consumption; and we document an increase in individuals' perceived freedom to express what they think, to join political organizations, to vote, and to voice their political opinions.
