The United Nations Security Council has, since the end of the Cold War, become a markedly more active player on the international stage. The number of resolutions adopted – in particular those adopted under Chapter VII of the Charter of the United Nations – the number of peacekeeping missions, and the use of mandatory sanctions have all increased considerably. The Council has also broadened its view of security, and adopted several resolutions that deal with thematic issues rather than with specific conflicts. In this study, we raise the question of whether this increased activity has been accompanied by a corresponding increase in the effectiveness of the Council. To answer this we analyse how the Council has developed its reaction to the use of force in inter-state relations. Under the United Nations Charter, prohibition of the use of force, other than in self-defence, is one of the most fundamental rules, and responsibility for upholding it rests with the Security Council. We conclude that despite the increased level of activity on the part of the Council since the end of the Cold War, its ability to react consistently and authoritatively to violations of the prohibition of the use of force has not been strengthened.