After a careful analysis of the law regarding the use of force in international relations and the practice of States since 1945, the author concludes that the United Nations Charter leaves no room for a “humanitarian intervention” in the internal affairs of a State. In his opinion NATO's armed intervention in the Balkans in the spring of 1999 therefore has no legal basis under the UN Charter. He goes on to say, however, that the question whether NATO's action against the Federal Republic of Yugoslavia may not be justified by an existing or an emerging rule of customary law should be examined. Such a discussion should take into account, on the one hand, the magnitude of the humanitarian disaster to be averted, and on the other hand the absence of objections by the Security Council or (with rare exceptions) by States. The author concludes with an appeal to the permanent members of the Security Council not to use their veto when deciding on action to be taken in the event of humanitarian disasters.