Differentiated European integration beyond mainstream approaches

Since the beginning of the 21st century, European studies have developed an interest in the analysis of ``variable geometry Europe''. This introduction proposes a critical dialogue with the mainstream theories of European integration which conceptualise ``horizontal'' differentiation (territorial variations) and ``vertical'' differentiation (variations in the centralisation of power from one public policy to another). A third logic of ``transversal'' differentiation is proposed to capture the professional groups working to build a variable geometry Europe thought as a social fact.