The articles in this special issue find ample evidence for the EU's influence on domestic and regional institutions. Its impact is patchy, often shallow but certainly not spurious. This conclusion demonstrates that it is worthwhile to integrate the Europeanisation literature and its theoretical arguments into the larger literature on diffusion. But it also shows limits of the diffusion approaches in the social sciences which tend to privilege structure over agency and, as a result, tend to focus on institutional convergence and isomorphism rather than variation in institutional outcomes. Some general impact of the EU on domestic institutional change in its neighbourhood and beyond is found, as well as some diffusion of EU institutional models of regional integration worldwide. The approach is decidedly agency-centred in focusing on diffusion mechanism and on scope conditions.