Unstable states in an unstable world generate a lot of threats to the peace. The task of the Security Council of the United Nations is to locate and eliminate threats to the peace and it has powerful means of enforcement at its disposal. The question is, what constitutes a threat to the peace in the view of the Security Council? Do crimes against human rights constitute a threat to the peace? Does a lack of democracy constitute a threat to the peace? Is the Security Council free to consider anything a threat to the peace as long as its permanent members can agree? The unprecedented activity of the Council during the 1990s has resulted in a large number of resolutions illustrating the way in which the Council interprets the notion of threat to the peace in the UN Charter. The resolutions have often been followed by enforcement action, sometimes in the form of military interventions. This book analyzes the practice of the Security Council with respect to the notion of a threat to the peace and the kind of action taken in response to such threats. In both respects the practice of the council is important but inconsistent.