Indeed, the Schengen agreements paved the way for Schengen visa waiver. Although this is not part of the initial provisions of the agreement, visitors from the fifteen aforementioned countries now only need a visa for all. The Schengen visa can allow non-members of the European Union to travel freely through the countries participating in the program. In many border crossings, there are special routes for EU, EEA and Swiss citizens (and their family members) and other routes for all travellers, regardless of nationality.  In some border crossing points, there is a third type of route for Travellers who are Annex II nationals (i.e.B. visa-exempt third-country/EEA/Swiss nationals).  Although Andorran and San Marines citizens are not EU or EEA citizens, they can nevertheless use the special routes provided for EU, EEA and Swiss citizens.  After Brexit, British citizens will not be able to use the EU track in the current state of the rules, unless such a right is negotiated in the Brexit agreement with the EU. The European Union forms a customs union and a VAT area. However, not all Schengen States or the entire territory of the Schengen States are part of the customs union or the VAT area. Some countries therefore legally carry out customs controls on illicit goods such as drugs. The French overseas departments of French Guiana, Guadeloupe, Martinique, Mayotte and Réunion, as well as the overseas collectivity saint Martin, are part of the European Union, but not of the Schengen area, so it is not possible to travel to these departments with a French Schengen visa.
EU rules on free movement apply, but each territory has its own visa regime for non-European nationals (EEA). While a visa valid for one of these areas is valid for all, the visa waiver lists differ.  A Schengen visa, even issued by France, is not valid for these territories. A visa for Sint Maarten (valid for travel on the Dutch side of the island of Saint Martin) also applies to the French page.  France also has several territories that are not part of the EU or the Schengen area.  These are French Polynesia, French South and Antarctica, New Caledonia, Saint Barthélemy, Saint-Pierre and Miquelon, as well as Wallis and Futuna. 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. Now that the Schengen Agreement is part of the acquis communautaire, it has lost for eu Member States the treaty status that could only be changed in accordance with its conditions. . . .