The United Nations Security Council has, after the end of the Cold War, become a markedly more active player on the international stage. The number of resolutions adopted – in particular resolutions adopted under Chapter VII of the Charter of the United Nations – the number of peacekeeping missions, and the number of mandatory sanctions regimes 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 paper, we raise the question of whether this increased activity has been accompanied by a corresponding increase in the effectiveness of the Council. We do this by analysing how the Council has developed its reaction to the use of force in inter-state relations. Throughout the existence of the United Nations, the prohibition of the use of force, other than in self-defence, has been one of the most fundamental rules that the Council is assigned the responsibility to uphold. 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.