While extensive research shows that policies and institutions spread across states through processes of diffusion, we know little about diffusion among international organizations (IOs). This article advances the state of the field by developing a novel approach for the study ofdiffusion among IOs. This approach consists of three components: a theoretical focus onconnectivity among IOs as pathways for diffusion; a conceptual differentiation between alternative types of convergence effects; and a methodological strategy combining dyadic and spatial analysis of diffusion. The article illustrates the usefulness of this approach through an empirical case: the diffusion of participatory governance arrangements among IOs, 1970-2010. The analysis shows that connectivity among IOs contributes to convergence, which typically is manifested through imitation of very specific institutional models. The article has implications both for the study of IOs and for the general study of diffusion.