Introduction : effectiveness of multilateralism in the field of collective security : Part I. Theoretical approaches to and historical developments of global governance in the field of collective security : global governance in the field of collective security: how to make multilateralism more effective; effectiveness and ineffectiveness of the UN Security Council in the last 20 years : a European perspective; a US perspective ; Part II. The UN Security Council : the reform of the UN Security Council: the EU's contribution to the effectiveness of the UN Security Council between presence and impact ; Part III. UN peacekeeping : UN peacekeeping missions during the past two decades; options for improving EU-UN cooperation in the field of peacekeeping ; Part IV. International peacebuilding and state-building : international peacebuilding and state-building efforts; building peace in post-conflict environments : why and how the UN and the EU interact; constructing a framework of effective multilateralism ; Appendix 1. the UN Security Council reform process: recent developments ; Appendix 2. joint declaration on UN-EU cooperation in crisis management ; Appendix 3. joint statement on UN-EU cooperation in crisis management ; Appendix 4. major stages of the institutionalization of the UN-EU cooperation ; Appendix 5. contributions of European states to UN peacekeeping operations ; Appendix 6. EU autonomous operation in support of a UN peace operations ; Appendix 7. operations involving UN-EU cooperation since 2003.