This paper reflects on the notion of differentiated integration in the context of the future of Europe. It argues that differentiation is only acceptable as an instrument of ‘unity in diversity’ and within strict limits. All forms of differentiation that risk fragmenting the Union and its institutional framework should be excluded. In the field of external policies existing treaties and the recent jurisprudence of the European Court of Justice allow the Union to speak with one voice and to privilege unity over differentiation. 

As far as internal EU divides are concerned– from divisions over migration to those involving the rise of regional groups of countries—they are all transient and changeable and are not relevant subjects for differentiation. Finally, attempts to redefine the euro area as the new ‘hard core’ of European integration should be rejected, as they can only lead to the disintegration of the European project. Out of all the available legal techniques of differentiation, enhanced cooperation carries the lowest risk.