The law is not static but is subject to continuous change. This applies to international law as much as it does to the municipal law of any state. International law can be modified by treaties and conventions, and by the development of new rules of customary practice. In this contribution the development of international law through the medium of the unauthorised conduct of international institutions will receive special attention.
It will be argued that provided the unauthorised conduct (a) is not expressly forbidden and (b) is acceptable to a cross-section of the international community of states, it can be the foundation of a new rule of customary international law. Two examples will suffice to prove the point, namely (a) the creation of ad hoc criminal tribunals by the Security Council of the United Nations, and (b) the military intervention of forces of the North Atlantic Treaty Organisation (NATO) in Serbia to put an end to the persecution of Kosovar Albanians by the repressive regime of Slobodan Milošević.