Convergence more or less: why do practices vary as they diffuse?

Much of the diffusion literature in international relations, international political economy, and comparative public policy focuses on explaining patterns of convergence among states, international organizations, and transnational organizations. This literature suggests that full or complete convergence is not a necessary or even likely outcome of diffusion processes. However, as of yet, findings of varying degrees of convergence remain largely context-specific and a more general and systematic review of the mechanisms explaining "how much" convergence occurs is still missing. To address this gap, this article offers a state-of-the-art review of studies describing and explaining the phenomenon. On that basis, we trace the occurrence of varying degrees of convergence back to differences in (i) the nature of the underlying diffusion model; (ii) the specificity of the diffusion item; (iii) the type of diffusion mechanism in operation; and (iv) the institutional context at the point of adoption.