Differentiation is a principle that has applied to the polity and policies of the European Union since its creation. It has been reinforced in the last 20 years as a consequence both of successive enlargements and of a broadening of the EU policy agenda. The British renegotiation process and the UK referendum scheduled for 23 June 2016 constitute a further stage in the debate on differentiation. For the first time a ‘no’ vote in a national referendum could mean that disintegration rather than differentiation is the preferred choice for an EU member state...