External differentiated integration: between stability and change

The external relations of the European Union (EU) are complex. Existing research has handled this complexity by approaching the EU’s external relations from a variety of distinct perspectives. The present special issue, by contrast, depicts the differentiated nature of the EU’s external relations as a feature of European integration that requires study and explanation in its own right. This introduction establishes a link between integration and external relations by drawing on the concept of external differentiated integration (EDI). After a discussion of the concept and theory of EDI, the introduction empirically shows how EDI has evolved over time at the macro-level, identifying periods of intensifying EDI and periods of relative stagnation. The article subsequently argues that this pattern confirms the existing literature on demand-side factors, but also points to the importance of supply-side factors, especially the nature of the international system.