The European Union (EU) consists of 28 member states. Each member state is party to the founding treaties of the union and thereby subject to the privileges and obligations of membership. Twenty-two of the twenty-eight European Union (EU) member states participate in the Schengen Area. Of the six EU members that are not part of the Schengen Area, four – Bulgaria, Croatia, Cyprus, and Romania – are legally obliged to join the area, while the other two – the Republic of Ireland and the United Kingdom – maintain opt-outs. The four European Free Trade Association (EFTA) member states, Iceland, Liechtenstein, Norway, and Switzerland, are not members of the EU, but have signed agreements in association with the Schengen Agreement. Three European microstates – Monaco, San Marino, and the Vatican City – are de facto part of the Schengen Area.