Regime complexity characterizes the international system, as many international organizations (IOs) overlap in membership and competencies at the same time. Unmanaged overlaps endanger the effectiveness of IOs. Inter-organizational cooperation can mitigate such negative consequences. However, a novel dataset reveals that not all overlapping IOs cooperate with each other and the institutionalization of cooperation agreements varies. Why do some but not all overlapping IOs opt for cooperation agreements, and why do their designs vary? The analysis of a demand–supply–restraint model shows that increased exposure to overlaps creates a demand for IOs to reach cooperation agreements and for their strong institutionalization. States respond more favourable to the supply of cooperation agreements when they are used to international cooperation and internal authority-delegation. The restraint component underscores that IOs are less inclined to cooperate when ideological differences and power differentials between them are greater and that IOs choose highly institutionalized cooperation agreements when their ideological differences are limited.

制度复杂性是国际体系的特征，因为许多国际组织（IO）在成员资格和职权方面同时重叠。不受管理的重叠会危及IO的有效性。组织间合作可以减轻这种负面后果。然而，一个新的数据集显示，并非所有重叠的国际组织都相互合作，而且合作协议的制度化也各不相同。为什么一些但不是所有重叠的国际组织选择合作协议，以及为什么它们的设计各不相同？对需求-供应-限制模型的分析表明，重叠风险的增加产生了对国际组织达成合作协议及其强有力的制度化的需求。当国家习惯于国际合作和内部权力授权时，它们会对合作协议的提供做出更有利的反应。克制部分强调，当国际组织之间的意识形态差异和权力差异较大时，国际组织不太愿意合作；而当意识形态差异有限时，国际组织会选择高度制度化的合作协议。