The international community has progressively tasked regional and sub‐regional organisations with conflict prevention and peacekeeping. This is largely due to an overburdened UN system. At the same time regional organisations have increasingly come to accept that violence, interstate and intra‐state wars normally affect the region through destabilizing spill‐over effects and that promoting peace is in their own best interest. Yet, it is argued in this report that regional organisations’ peace and security functions still do not amount to an effective regional conflict management regime. Furthermore, not all regional and sub‐regional organisations have begun to take on this responsibility. The introductory chapter by Herbert Wulf summarizes the reasons why regional organisations have played such a marginal role in the past and illustrates this with examples from different regional organisations. Particularly the African Union and several sub‐regional organisations in Africa are now taking on this newly ascribed role while the members of other organisations (particularly within ASEAN and ARF) remain reluctant to give up national sovereignty rights and to imbue the organisation with a peacekeeping role. The conclusion is that the role of regional organizations in conflict prevention and conflict management has been strengthened in recent years but that severe weaknesses, particularly the lack of common values within regional organizations and their lack of capacities, still limit their conflict prevention role. This INEF report also presents two case studies on the potential and the limits of a peace supporting role of regional organisations. First, Francine Jácome gives an overview of the role of the Organisation of American States (OAS) and several sub‐regional organisations in Latin America and the Caribbean and describes their conflict prevention role. This case study illustrates how important these organisations have been in preventing and resolving conflict. At the same time, the work of the OAS has suffered time and again from fundamental political differences within the organisation. The other case study on the conflict in Timor‐Leste by Akihisa Matsuno shows how irrelevant ASEAN and the ASEAN Regional Forum have been in this conflict. It was mainly the UN and a “coalition of the willing” under Australian leadership who reacted to the conflict in Timor‐Leste. Matsuno discusses the structural deficiencies of the political system that led to the crisis and argues that the main task of the UN transitional administration, the building of a functioning democracy, was not achieved and local institutions were too weak and too much in competition to establish a fully functioning state.