In Resolution 1373 the Security Council laid down a series of general and abstract rules binding on all UN member states. In doing so, the Council purported to legislate. This article discusses whether it is entitled to do so. In the light of the Charter and the past practice of United Nations organs, it argues that the Council can only exercise its Chapter VII powers in response to specific situations or conduct. In enacting Resolution 1373 the Council acted ultra vires. The article looks at the circumstances in which such an extension of the Security Council's powers might be acceptable, but concludes that unilateral attempts by the Council to legislate would be destructive of the international legal order.