Enhanced Cooperation, EMU Reforms and Their Implications for Differentiation in the European Union

Initially, before the entry into force of the Maastricht Treaty, differences in integration between members of the European Communities (EC; later the European Union) were relatively few and usually temporary in nature. The Schengen Agreement, the Maastricht Treaty and the Treaty of Amsterdam, and the possibility of establishing enhanced cooperation meant that the problem was becoming more and more important in the functioning of the EU—both in theory and in practice