The thesis examines the global institutional responses to the peace movement demands after the Cold War. The primary analysis revolves around several international campaigns carried out by coalitions of NGOs and other civil society organizations in the field of human security. Each empirical chapter examines the process towards the signature of a treaty largely from the activists’ perspective intertwined with diplomats and UN officials' views. The identification of pathways and determinants of successes and failures in these processes forms the central part of the analysis. The cases of study are the Coalition to Stop the Use and Recruitment of Child Soldiers, the International Campaign to Ban Landmines, the International Action Network against the proliferation of Small Arms and Light Weapons, and the Coalition to stop Cluster Munitions. The strategic and organizational levels of these networks are examined through their roles in each international negotiation context, such as the Conference of Disarmament, the Convention of Certain Weapons of the UN Program of Action of Small Arms or the Oslo Process on Cluster Munitions. From this perspective, different successes can take place in terms of the access to the institutions and the procedures of the bargaining processes, in the setting of the (political and media) agenda and in the legal and policy-making dimension. In the long term, the model also considers the existence of cultural effects. The assessment of these effects is carried out mainly from a qualitative point of view. In the thesis, there are three cases that are successful (that result in a treaty) and one unsuccessful case (small arms), although each of them has a different degree of success in different dimensions, ensuring therefore the variability of the dependent(s) variable(s). This analysis in turn raises many more themes and inevitably a great host of questions. Among these is an investigation of a common pattern of evolution of a transnational coalition through three phases: the creation of the coalition, the negotiation of the treaty and its implementation. The lessons of these campaigns suggest that civil society organizations can be politically influent under a set of conditions, including flexible rules of the game (e.g. voting by majority and participatory channels) and a solid and credible leadership by allied countries willing to spend resources and organization in an issue that has humanitarian effects. Moreover, the most effective coalitions know how to better use the different contexts favourable to collective action, and also how to combine their resources (research, experience, grass-roots membership and the media), strategies (protest and political pressure, but also communicative processes, such as framing the problem and shaming the irresponsible governments), a flexible organization and the capacities of their international allies. Sometimes also, external events, such as changes in a government, terrorist attacks or economic crisis can play a role in these processes.