The free movement of persons is a fundamental right guaranteed by the EU to its citizens. It entitles every EU citizen to travel, work and live in any EU country without special formalities.
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 border-free Schengen Area guarantees free movement to more than 400 million EU citizens, as well as to many non-EU nationals, businessmen, tourists or other persons legally present on the EU territory.
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 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.
The UK and Republic of Ireland have opted out. The UK wants to maintain its own borders, and Dublin prefers to preserve its free movement arrangement with the UK - called the Common Travel Area - rather than join Schengen.
The UK and Ireland began taking part in some aspects of the Schengen agreement, such as the Schengen Information System (SIS), from 2000 and 2002 respectively.
The SIS enables police forces across Europe to share data on law enforcement. It includes data on stolen cars, court proceedings and missing persons.