This paper examines the rise of conflicts over the extraction of natural resources in the developing world. It emphasizes the main factors that motivate collective action: threats and opportunities. Challengers join in action to avoid the adverse socio-environmental effects associated with extraction, but they also mobilize because of new opportunities or advantages that extraction brings to host communities. These incentives are most likely to trigger collective action at the local level but can also prompt the participation of outside groups, depending on the nature of the threat. Mobilization strategies are partly shaped by the local conditions where mining is taking place; preventive mobilization is favored in some areas and the judicialization of conflicts in others. This paper draws on two extractive conflicts, the Tía María copper project in Peru and the Fuleni coal project in South Africa, to illustrate the drivers of collective action, the nature of mobilizing methods, and the impact of these methods on the cancellation of the projects. It concludes by discussing the long-term impact of mobilizing strategies on extractive conflicts.