The Maastricht Treaty, signed in 1992 and ratified in the following year, is widely seen as a landmark in the evolution of the European Union. It introduced into the treaty framework revolutionary new elements such as the co-decision procedure between the Council and the European Parliament, cooperation in the area of Justice and Home Affairs, the Common Foreign and Security Policy and the "euro" as a single currency for the majority of the then member states. It also introduced the concept of European citizenship into the treaty, reflecting the rising expectations of both citizens and decision-makers in the European project, and upgraded the role of the European Council at the summit of the EU’s institutional structure. Twenty years later...