In this dissertation, I ask: Which attributes of intergovernmental organizations (IGOs) are conducive to member state interest convergence? Scholars testing the effects of IGOs on state behavior usually control for state interests in order to counter realist arguments. However, by doing so, they may be missing one channel through which IGOs ultimately affect state behavior - through changes in state interests. While research on socialization informs the study of interest convergence, it is insufficient to answer the question of which attributes of IGOs make them conducive to state interest convergence. These studies consist largely of case studies with which one cannot easily control for material factors that affect member state interests and they focus on the induction of new member states into an existing community. I argue instead that all states are subject to the acceptance of ideas (both normative and cognitive) that can affect how they define their interests and that it is more appropriate to look at pairs of states to assess their interaction affects their similarity to each other.I argue that greater interaction between member states provides more opportunities for the transmission of ideas between them and therefore greater convergence in how they define their interests. I therefore expect IGOs with more substructures and covering more issues to be more conducive to interest convergence. I also propose that different types of similarity between states (regime type and cultural similarity) can make states predisposed to the acceptance of ideas from one another and thus enhance the degree to which intra-IGO interaction may lead to interest convergence. The aforementioned hypotheses are tested in statistical models, using an original dataset of IGOs or IGO structures as the key independent variables. The findings provide support for the theory that more interaction within IGOs leads to greater interest convergence. The findings with regard to dyadic attributes are mixed, providing support for the idea that dyads with common cultural attributes experience greater interest convergence as a result of interaction within IGOs than other dyads, while domestic regime type similarity has the opposite effect to that expected