The article discusses the impact of recent military interventions in Kosovo, Afghanistan and Iraq on the rules governing the use of force in international law. It argues that, in spite of some egregious violations, existing rules have not been changed or fallen into desuetude. The attempt to dismantle the collective security system and the claim to relax beyond recognition the general prohibition on the use of force have found the strong opposition of the overwhelming majority of the UN membership. Furthermore, existing rules and Article 51 of the UN Charter have proved flexible enough to protect States against the threats posed by terrorism and weapons of mass destruction. Their application, nonetheless, remains extremely problematic and confirms the need for a collective control over the use of military force.