This paper attempts to go beyond actor-centered explanations of the European Union's (EU) presence in regulatory politics by examining the role of the EU in the diffusion of regulatory norms and practices. We explore the international diffusion of public procurement policy, to which multiple organizations and especially the EU and the World Trade Organization have made an active contribution. Using the “opportunity-presence-capability” scheme, we argue that the EU is actively co-shaping the global agenda on public procurement, mainly as a result of the “opportunity” and “presence” dimensions of its global actorness and its role in the horizontal diffusion of public procurement regulations between international organizations. For “EU as a global actor” literature to offer valuable explanations, an in-depth analysis of its relationship with other international organizations, such as the World Trade Organization, reveals significant interactions and the co-shaping of policy agendas. © 2017 John Wiley & Sons Australia, Ltd