Of the 27 EU Member States, 22 participate in the Schengen area. Of the five EU Member States that are not part of the Schengen area, four – Bulgaria, Croatia, Cyprus and Romania – are legally obliged to join in the future, while the other – Ireland – maintains an opt-out. The four member states of the European Free Trade Association (EFTA), Iceland, Liechtenstein, Norway and Switzerland, are not members of the EU, but have signed agreements related to the Schengen Agreement. Three European micro-states that are not members of the European Union, but are enclaves or half-slaves within an EU member state – Monaco, San Marino and Vatican City – are de facto part of the Schengen area. Normally, a passport or European identity card is required. Greece, Iceland and Malta do not share land borders with other Schengen Member States. In 1999, the United Kingdom formally requested participation in certain provisions of the Schengen acquis – Title III on police security and judicial cooperation – and in 1999 this request was approved by the Council of the European Union on 29 May 2000.  The UK`s formal participation in previously approved areas of cooperation was implemented by a 2004 Council Decision, which entered into force on 1 January 2005.  Although the UK was not part of the passport-free Schengen area, it nevertheless used the Schengen Information System, a government database used by European countries to store and disseminate information about individuals and goods. This has allowed the UK to exchange information with countries that are part of the Schengen Agreement, often to agree on legal proceedings.  In 2020, the United Kingdom stated that it would withdraw from these agreements at the end of its transition period. There is no doubt that there are very strict qualification criteria that must be met in order to become a Schengen country, such as showing how they can assume responsibility for controlling the region`s external borders and how they use the Schengen Visa Information System.
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