States in western Europe who have chosen, for various reasons, not to become full members of the EU have integrated with it to different extents according to their circumstances. Iceland, Norway and Liechtenstein participate directly in the single market via the European Economic Area, Switzerland does so via bilateral treaties and the other European microstates (Andorra, Monaco, San Marino, Vatican City) have specific agreements with the EU and neighbouring countries, including their use of the euro as their currency. Most of these countries are also part of the Schengen Area.