Constitutional ‘documents’ is exactly the problem. The EU is a very large (as of January 2007, 27 member states) international organisation with a considerable number of competencies and several important institutions. It is important to have one, clear document that precisely defines the different powers of, and relationships between the 27 member states, the European Commission, the European Parliament and the Courts of Justice. But also the relationships between states that may have opted out of some parts of the EU; between those who are in Schengen and those who opted out, between those in the Eurozone and those outside. Complicated federal polities such as the United States, Germany and Switzerland have constitutions which define the limits of central power and the areas in which the states have autonomy; the EU should in this respect be no different.