We conceive authority of an international organization as latent in two independent dimensions: delegation by states to international agents and pooling in collective decision making bodies. We theorize that delegation and pooling are empirically as well as conceptually different. Delegation is an effort to deal with the transaction costs of cooperation which are greater in larger, broader, and correspondingly more complex organizations. Pooling reflects the tension between protecting or surrendering the national veto. This paper theorizes that delegation and pooling are constrained by two basic design features: a) the scope of an IO’s policy portfolio and b) the scale of its membership. We test these hypotheses with a new cross-sectional dataset that provides detailed and reliable information on IO decision making. Our major finding is that the design of international organizations is framed by stark and intelligible choices, but in surprising ways. Large membership organizations tend to have both more delegation and more pooling. The broader the policy scope of an IO, the more willing are its members to delegate, but the less willing they are to pool authority.