Over the last two decades, courts in Latin America and in other developing democracies have become increasingly involved in the policy making process. High courts in Brazil, Colombia, Argentina, Peru and Costa Rica have issued rulings expanding socioeconomic rights, curbing executive excesses and protecting the rights of minorities. Current scholarship focuses on discerning why some courts and not others get away with making these controversial judgments. Yet, we know little about the implementation and, more broadly, the impact of these decisions. This project addresses this understudied phenomenon. Under what conditions can courts in new democracies produce effective political and social change? More specifically: Why do some rulings have significant influence on public opinion, the mobilization of activist coalitions or policy outcomes? Why is there variation in compliance with judicial rulings? This project will study the impact of high court decisions on socioeconomic rights in Colombia and Peru. I argue that explaining impact requires paying attention to the courts’ oversight mechanisms (committees, public hearings, information requests etc.) and to the presence of a legally empowered constituency in civil society. To evaluate the role of oversight mechanisms and legal constituencies in promoting impact, I will conduct a ‘within and across’ paired comparison of major rulings by the Colombian and Peruvian highest tribunals in three social policy areas—environment, health and social welfare. Empirically, the project will generate original data on the processes following selected major rulings to assess a) the indirect effects of these rulings (including their influence on the following: public opinion, on incentivizing mobilization and on changing the behavior of governmental and private actors not directly affected by them); b) efforts at compliance and implementation over time; and c) policy results.