Why do some protests call for moderate reforms while others demand regime change? This distinction was evident during the Arab Spring, when some countries primarily experienced ‘radical’ protests demanding regime change and others only experienced calls for reform. This project seeks to explain why protest groups call for regime change, rather than reforms. Existing work on the adoption of radicalism tends to rely on structural explanations, such as relative deprivation or modernization. However, other research suggests that the relative position of individuals within their social group is more relevant in predicting adoption of radical beliefs. As such, it is argued protests making (radical) demands for regime change are a result of organization by new political movements, which rely on individuals that are isolated from a country’s political culture. While established political movements can draw on long-standing supporters to attend protests, new political movements lack the organized base that would turn out to protest for particular cause. Instead, new movements must rely on protest attendees who are not socialized in the political system and are more likely to express opposition to the government in absolute terms. It follows that more politically socialized individuals should be more likely to participate in moderate protests, while those who are not should be more likely to join radical protests. The theory is tested at both individual and group levels. At the individual level, a survey experiment of Lebanese adults is conducted to explain the effect of political socialization on participation in either moderate or radical protests. Some respondents are primed with a question about the Lebanese government's worst policy, intended to channel negative sentiment toward the government into a specific grievance. Then, respondents are asked whether they would participate in either moderate or radical protests. The findings show that respondents who receive the socialization prime are more likely to participate in moderate protests, while those who do not receive the prime are more likely to participate in radical protests. A group-level test is conducted using original data on protests, protest demands and participants gathered from 19 Arabic-speaking countries between 1992 and 2014. Findings show that protests without clear organizing groups or organized by groups that recently entered a country's political arena are more likely to call for regime change. Cumulatively, results suggest that political socialization plays a key role in both shaping individual protest participation and group-level protest demands across the Arab World.