The Schengen area originally had its legal basis outside the European Economic Community at the time, since it was created by a subgroup of Community Member States with two international agreements: 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 required to join the territory 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 under the Schengen Agreement. Three European micro-states that are not members of the European Union, but which are enclaves or half-enclaves within an EU member state – Monaco, San Marino and Vatican City – are de facto part of the Schengen area. Ireland participates in some police cooperation agreements that are part of the Schengen Agreement. From 2020, Ireland will participate in some aspects of SIS II, the second generation of the Schengen information system – see “Police and Security” below for more information. Vatican City has an open border with Italy. In 2006, it expressed interest in joining the Schengen Agreements with a view to closer cooperation on the exchange of information and similar activities under the Schengen Information System.  Exceptionally, Italy allowed people to visit Vatican City without being accepted for an Italian visa, and then to be escorted by police between the airport and the Vatican or by helicopter.
[Citation required] However, there is no customs union (including customs) between Italy and the Vatican, so all vehicles are controlled at the Vatican`s borders. The Republic of Ireland, also known as Eire, is not part of the Schengen area, but it is part of the EU. In fact, Ireland is only one of the few EU countries that have never joined Schengen. This makes it a little disconcerting for many people, including many Europeans. The Schengen agreement must provide uniform border rules for all countries in the zone. As soon as you are allowed to enter a Schengen country, you can travel to one of the other countries as long as you do not exceed the maximum of 90 days throughout the zone. At many external border crossing points, there are special routes for EU, EEA and Swiss citizens (as well as family members) and other routes for all travellers, regardless of nationality.  At some border crossing points at the external border, there is a third route for Schedule II travellers (i.e. third-country/EEA/Swiss nationals who are exempt from the visa requirement).  Although Andorran and San Marines citizens are not EU or EEA citizens, they may use special routes for EU, EEA and Swiss citizens.
 British citizens will not be able to use the EU`s trace after Brexit under current rules, unless such a right is introduced into the Brexit deal with the EU. In 1999, the United Kingdom formally requested participation in certain provisions of the Schengen acquis – Title III on police security and judicial cooperation – in 1999, and this request was adopted by the Council of the European Union on 29 May 2000.  The UK`s formal participation in previously approved areas of cooperation was brought into effect by a 2004 Council decision that came into force on 1 January 2005.  Although the United Kingdom was not part of the Schengen area, it has always used the Schengen information system, a government database used by European countries to store and disseminate information on individuals and goods. This has allowed the UK to exchange information with countries that are part of the Schengen Agreement, often to connect to legal proceedings.  In 2020, the United Kingdom has declared that it will withdraw from these agreements at the end of its transition period.