The Schengen Treaty is an international treaty on people’s freedom of movement, which provides to abolish border controls.

Schengen is joined by 26 Countries, whose twenty-two are EU members, and four are non-members (Iceland, Liechtenstein, Norway and Switzerland). Ireland and the United Kingdom, exercised the opt-out clause, thus not adhering to the Treaty. For Bulgaria, Cyprus, Croatia and Romania Schengen has not entered into force yet.

 

The area of free movement has gradually entered into force since 1985, when France, Germany and the Benelux countries signed the agreement. Italy joined in 1990.

The agreements became part of the EU rules in the Treaty of Amsterdam, and were later incorporated into the Maastricht Treaty.

 

The Treaty provides the abolition of border controls within the Schengen area, the strengthening of external border controls, collaboration between police forces and operations beyond the borders of Sates, the coordination between States in the fight against  international organized crime, and integration of  police’s databases.

 

Because of recent terrorist attacks in Paris on 13 November 2015, and in order to counter the arrival of asylum seekers and migrants, some countries (Austria, Denmark, France, Germany, Norway and Sweden) have suspended the operation of the Treaty, thus reintroducing checks for people at borders.

Under EU's southern countries pressure, such as Greece and Italy, it is being discussed to suspend the Treaty and to reinsert the internal border controls up to two years. The clause can be applied only if there is a "serious threat to public order and internal security", or "serious deficiencies related to external border control" that could endanger "the overall functioning of the Schengen area."