This thesis focuses on a particular aspect of the international role of the European Union (EU), examining the evolution of EU conflict prevention policy in the post- Cold War period. In recent years the EU has extended its range of external relations policies, and conflict prevention has emerged as a prominent objective on the agenda, particularly as the Union faced political and economic instability on its borders. After introducing conflict prevention and analysing the EU's external relations and the post- Cold War security context, the thesis examines the EU's institutional set-up for conflict prevention. The incremental development and institutional structure of the EU renders the formulation and implementation of conflict prevention by the EU a particular challenge. The thesis then proceeds to an investigation of EU cooperation and conflict prevention policy coordination with the security organisations identified as the EU's key partners: the United Nations (UN), the Organisation for Security and Cooperation in Europe (OSCE) and the North Atlantic Treaty Organisation (NATO). While post-Cold War conflict prevention requires a multilateral approach, the proliferation of European security organisations and the increasing overlap in their objectives makes policy coordination between the EU and other organisations particularly important. It is concluded that the EU faces fundamental internal coordination problems and institutional divisions in its elaboration of conflict prevention policy. Conflict prevention is underdeveloped by the EU and is in danger of being marginalised in favour of shorter-term crisis management. Furthermore, internal coordination problems have a detrimental impact on the organisation's ability to cooperate externally with other security organisations. EU external priorities in conflict prevention focus on cooperation in crisis management with the UN and NATO, and fail to capitalise on the advantages of cooperation with the OSCE. The failure of the EU to fully adopt conflict prevention as an external relations priority and to coordinate its activities with other organisations could have implications for future stability in, and on the borders of, the EU.