We study international regimes because we are interested in understanding order in world politics. The theory of hegemonic stability is that the concentration of power in one dominant state facilitates the development of strong regimes, and that fragmentation of power is associated with regime collapse. But fluctuations in demand for international regimes are not taken into account by the theory. However, considering the supply is not of much importance, as the article focuses mainly on the demand of regimes to provide the basis for a better interpretation. It is therefore a systemic theory: the author uses the rational-choice theory to develop models that help to explain trends or tendencies toward which patterns of behavior. The context and functions of international regimes: two features of the international context are particularly important: world politics lacks authoritative governmental institutions, and is characterized by uncertainty. If all these conditions were met in world politics, ad hoc agreements would be costless and regimes unnecessary.