Signs being taken down on the German-Czech border
The Schengen Agreement abolishes internal borders, enabling passport-free movement between a large number of European countries.
The BBC News website explains what the Schengen Agreement consists of and how it came about.
Which countries have removed internal borders?
On 12 December 2008, the number increased to 25.
Belgium, France, Germany, Luxembourg, the Netherlands, Portugal and Spain implemented the agreement in 1995. They were followed by Italy and Austria in 1997, Greece in 2000, and Denmark, Sweden, Finland, Norway and Iceland in 2001.
Nine more members joined in 2007, they are the Czech Republic, Estonia, Hungary, Lithuania, Latvia, Malta, Poland, Slovakia and Slovenia. Switzerland implemented the agreement on 12 December 2008.
Are other countries going to remove them too?
Liechtenstein expects to implement the agreement on 1 November 2009. There is no date yet for Cyprus which joined the EU in 2004 or for Bulgaria and Romania, which joined in 2007.
The latter two countries are not yet deemed to meet the necessary security criteria.
What else, apart from removal of internal borders, does Schengen involve?
The main feature is the creation of a single external border, and a single set of rules for policing the border. Among the other measures are:
- Common rules on asylum
- Hot pursuit - police have the right to chase suspected criminals across borders
- Separation in airports of people travelling within the Schengen area from other passengers
- Common list of countries whose nationals require visas
- Creation of the Schengen Information System (SIS) which allows police stations and consulates to access a shared database of wanted or undesirable people and stolen objects
- Joint efforts to fight drug-related crime
In what circumstances can countries re-impose border controls?
Under article 2.2 of the treaty, signatories may reinstate border controls for a short period, if this is necessary for national security reasons.
France did this around the 60th anniversary of D-Day in June 2004 and after the bomb attacks on London in 2005. Portugal, Finland and Germany have all re-imposed border controls for major sporting events such as the 2006 Fifa World Cup.
How are non-EU citizens affected?
A Schengen visa is necessary to travel to a Schengen country or within the area. The price of a short stay visa is 60 euros and for some Europeans will mean a substantial extra cost. Belarussians had been used to paying only 5 euros for a trip to neighbouring Lithuania.
The cost of the visa will be lower (35 euros) for Russians, Ukrainians and citizens of non-EU Balkan states. But it still means greater inconvenience.
Americans living in the Czech Republic have until now required no more than a tourist visa which had to be renewed every 90 days with a short trip to neighbouring Germany or Austria.
Now they will have to apply for the new visa at an embassy outside the Schengen zone, and the closest are in Switzerland, Ukraine and Romania.
Why is it called the Schengen Agreement?
This is the name of the town in Luxembourg, where it was signed in 1985. Actually, the signing itself took place on a boat in the middle of the Moselle river, which forms the border between Luxembourg and Germany.
The Convention applying the Schengen Agreement took another five years to negotiate and there was a further time-lag before the convention was implemented.
Is Schengen an EU initiative?
It began as an attempt to give practical meaning to the European Union's longstanding goal of ensuring "free movement of persons".
However, while all countries agreed that there should be no border checks on EU nationals, they could not agree whether non-EU nationals should enjoy the same privileges when travelling inside the EU.
As a result, the Schengen agreement was originally signed outside the auspices of the EU (by France, Germany and the Benelux countries).
It was incorporated into the framework of the EU as part of the Amsterdam Treaty in 1997. The European Commission took over the administration of the agreement from the previous Executive Committee.
Which EU countries are not party to the Schengen agreement?
The UK and Ireland have opted out. The UK wants to maintain its own borders, and Ireland prefers to preserve its free movement arrangement with the UK - called the Common Travel Area - rather than join Schengen. However the introduction of an electronic border system expected in 2009 may require travellers between the two countries to carry passports.
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.
Cyprus, Romania and Bulgaria have not agreed dates to join the scheme.
Andorra and the German islands of Heligoland fall outside the treaty.
What is the Schengen Information System?
The SIS enables police forces across Europe to share data on law enforcement. It can cover stolen cars, court proceedings and missing persons. The enormous SIS database, in the French city of Strasbourg, is due to become even larger with the introduction of SIS II.
That would enable police to link information such as alerts involving a missing child and a stolen car. The UK says it will only sign up to SIS II once it is happy the system works alongside the Police National Computer.
Which signatory countries are not members of the EU?
Iceland, Norway, Switzerland and Liechtenstein. Iceland and Norway participate in drafting new measures introduced as part of the chengen system. The Swiss, too, have decision-shaping, but not decision-making, powers. The acts are formally adopted by the EU states alone.