The Schengen Area is a passport-free travel zone made up of 26 nations
What is the Schengen Area?
The Schengen Area is a visa-free travel zone made up of 26 European nations – 22 EU states and four other nations Iceland, Liechtenstein, Norway and Switzerland.
Citizens from these countries are permitted free movement of travel inside the area’s single external border because the internal borders have been abolished.
The UK and Ireland have chosen to opt out of the zone, while Bulgaria, Croatia, Cyprus and Romania are legally obliged to join following their accession to the EU.
As well as passport-free travel, the Schengen Agreement also demands nations adopt common rules on migration, allowing refugees and those on visas to move freely.
This agreement also allows police to chase suspected criminals across borders and access a shared database of wanted people and stolen objects.
The Schengen Agreement was signed on 14 June, 1985 and was named after the town in Luxembourg where the signing took place.
The first member states were Belgium, France, Germany, Luxembourg and the Netherlands.
Is the Schengen Area doomed?
Schengen has come under fire for allowing migrants and home-grown terrorists to pass through borders unchecked.
Many nations have chosen to reintroduce border controls after the influx of more than a million migrants and the terror attacks in Belgium, Germany and France.
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Just six of the EU's member states are not a part of the zone
The Schengen Agreement allows states to reinstate checks for reasons of “public policy or national security” for up to 10 days.
This can be extended for up to a maximum of two years in “exceptional circumstances”.
Currently seven countries have border checks in place: Austria, Denmark, France, Germany, Norway, Poland and Sweden.
Many leaders have called for the end of Schengen, saying it is the only way to combat terrorism and end the migrant crisis.
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Theresa May met with leaders from Northern Ireland to discuss the CTA
How will Brexit affect the British-Irish border?
Brexit will not have any impact on the Schengen Agreement because the UK and Ireland have never been a part of the Schengen Area.
Nobody wants to return to the borders of the past
Theresa May
But there have been questions on whether Brexit will mean the reintroduction of borders between Northern Ireland and the Republic - something Theresa May has ruled out.
Britain and Ireland currently have their own free movement arrangement, called the Common Travel Area (CTA) Currently, both countries allow EU nationals to enter freely.
After Article 50 has been triggered, Britain will have to negotiate trade deals with the EU and other countries around the world.
