The United Nations has widened progressively the scope of its action in post-conflict situations, and has included efforts in economic reconstruction, by creating the Peacebuilding Commission in 2005. It is not only about peacekeeping, but also about reviving the economy of conflict-affected countries. Peacekeeping missions in Liberia or Sierra Leone have thus integrated an economical dimension ; whereas in Kosovo, the UN has placed the territory under international administration, and in Iraq the UN mission has focused on economical aspects. The question remains: which legal framework would best confer legitimacy and legality to the UN economic actions ? Logically, the UN should rely upon the WTO economic international law. But the relations between international law and economic international law are yet to be figured out.