In the past decade, several events have provided the backdrop for a great public debate about the legality of the use of force by states in international relations. Military actions in Kosovo, Afghanistan, Iraq and Lebanon have increased public awareness of, and thus the political consequences of, the legal arguments for and against the use of force by states. Meanwhile ongoing conflicts in Africa and the Caucasus region have served as a reminder that the use of armed force by irregular and guerrilla forces are still as much a part of conflict today as the proxy wars that occurred during the Cold War. Notwithstanding the prohibition on the threat or use of force contained in Article 2(4) of the Charter of the United Nations, the UN itself has observed that military force has been used hundreds of times since 1945.2 So clearly, the use of force by states to resolve problems and conflicts is alive and well. Does this mean conversely that Article 2(4) is dead as Thomas Franck controversially suggested almost 40 years ago?3 It is doubtful that any state would claim that it still possesses a nineteenth-century style legal right to go to war when it considers it in its national interests. It is also not a stretch to claim that the vast majority of states and most academics would agree that the use of armed force for aggressive purposes is illega1. 4 However, force is still being used with regularity. Certainly, not all uses of force since 1945 have been legal given any reasonable interpretation of the post -Charter state of the law regarding the use of armed force. At the same time, it is also difficult to see how they could all be illegal. The legal tension is not to be found in the general prohibition on the use of force, but rather is located in the primary exception thereto, namely, self-defence.5 Article 2(4) is not dead, but Article 51 is struggling.