This chapter discusses the ways in which collective identity fuels mobilization in Chile’s urban margins. It looks at how activists’ cohesiveness and their differentiation from other social actors produce a mobilizing identity that advances contentious politics. The chapter draws on participant observations and interviews to outline the contents and dynamics of political consciousness production in Santiago’s urban margins. In their interactions, activists wield discourses of informality and marginality to strengthen a sense of pride in their neighborhood that is immune to hegemonic narratives of stigmatization. The thick boundaries that local activists use to promote mobilization depend on them dynamically differentiating between two realms of collective experience: the formal and the informal. On the one hand, the informal represents the protected sphere of confidence and close connections within neighborhood organizations. Activism works as a way of keeping the informal alive. The formal, on the other hand, is seen as a threat that motivates protective collective action. Finally, the chapter shows how activists’ reactive and defensive mobilization generates a sense of self-determination.