Under what conditions does a social movement have an impact on state policy and gets their main demands addressed? This dissertation explores these questions through a structured and focused comparison of two social movements in three Latin American countries: Argentina, Chile and Uruguay. The cases analyzed in this project are the human rights movement and their demand for justice for the past abuses of the military dictatorship, and the women's movement demand for the decriminalization of abortion from the time of each country's democratic transition until 2007. This dissertation argues that for non bread and butter issues to be addressed by the government a social movement organized around them must be present. The movement has to be strong in terms of its power to attract supporters, since it is mainly responsible for placing the issue on the political agenda. Non-bread-and-butter issues such as those espoused by the social movements studied here are not considered a priority by public opinion in developing countries, and thus have a hard time reaching the political agenda if no movement mobilizes behind them. In addition, the social movement needs political allies in power for the issues to move forward: for bills, once introduced, to be debated and passed in Congress, for government programs to be implemented, and for institutions to be created that address the movements' demands. Finally, not all those politicians ideologically close to the movement will respond to its demands in the same way. Political and strategic considerations play a role here. The weaker the president is when assuming power and in particular the greater the need for support from leftist constituencies, the more the government will try to advance the main demands of these social movements.