This special issue explores to what extent policies and institutions of the European Union spread across different contexts. Are the EU's attempts to transfer its policies and institutions to accession and neighbourhood countries sustainable and effective? To what degree do other regions of the world emulate the EU's institutional features; what are the mechanisms of, and scope conditions for, their diffusion? This introduction provides the conceptual framework of the special issue. First, it specifies EU-related institutional change as the ‘dependent variable’. Second, it discusses how Europeanisation research and diffusion studies relate to each other and can be fruitfully combined to identify processes and mechanisms by which ideas and institutions of the EU spread. Third, we introduce scope conditions which are likely to affect domestic (or regional) change in response to the promotion or emulation of EU ideas and institutions.