The Schengen area represents an area of free movement for citizens between the 26 signatory states of the Schengen Agreement (held in the city of Schengen in Luxembourgon the 14th June 1985). 22 of the 28 members of the European Union are now part of the Schengen area.
Since 1995, the Convention implementing the Schengen Agreement has been in force: border controls between the signatory states have been abolished. Only a single external border exists. Thus, all signatory countries apply a common policy on visas and controls at the external borders of the area are strengthened. A Schengen visa issued by a Member State is valid for the whole Schengen area.
Here’s a list of those countries :
Within the Schengen area, the principle of the free movement of people applies. Any individual, whether a national of the European Union or a third country,once they have entered the territory of one of the Member States, can cross the borders of the other countries without being subject to controls. Today you are in Barcelona and tomorrow you want to go to Paris? Move along, you’re free to go!
Which is an opportunity on so many levels, for the citizens of the signatory countries in one hand and the Tourists obtaining a Schengen Visa on the other hand, but an even greater opportunity for a person whose country’s citizens aren’t required to apply for a Visa at all to access the Schengen area (They will only need an ETIAS-an electronic travel authorization like ESTA for the USA or eTA for Canada- starting from 2021).
This is a map showing the European continent’s territory. As we can see the United Kingdom and Ireland are in fact EU states but not Schengen, which means that they are part of the European Union, but aren’t signatory of the Schengen agreement and are keeping their borders, vice versa is the case for Norway, Iceland, Switzerland and Liechtenstein, who aren’t members of the European Union but included in the Schengen agreement. These 4 are joining the other 22European Union countries allowing people’s movement inside both dark and light blue countries shown in the map. Other countries are shown as Schengen candidates (Green), these states wish to be part of the Schengen agreement but aren’t yet.