The Schengen Agreement was originally signed in 1985 with the principle purpose of abolishing border checks between signatories. It evolved from an independent agreement between five states to become a fundamental part of European Union law for the free movement of people.
At the time, the EU was still known as the European Economic Community. Still, there was disagreement on the abolition of border checks.
Belgium, the Netherlands, and Luxembourg already had their own borderless treaty, but they signed a border waiver with France and West Germany.
In 1990, the agreement was revisited and changed to the Schengen Convention, which introduced total abolition of internal border checks and a common visa policy.
The Schengen Treaty, signed near the village of Schengen in Luxembourg, was initially independent of European Union law. However, after the Amsterdam Treaty was signed in 1999, the Schengen Treaty was incorporated into EU law and transposed into the national law of Member States.
At present, 26 countries have signed the Schengen Treaty, including Malta. Only two EU Member States opted out of the Schengen Treaty: the Republic of Ireland and the United Kingdom. The treaty covers a population of over 400 million people and a land area of 4,312,099 square kilometres.
Bulgaria, Croatia, Cyprus and Romania are not yet members of the Schengen Area. Iceland, Norway and Switzerland are the three non-EU members who signed bilateral agreements with the bloc to become part of the Schengen zone. Micro-states Monaco, San Marino and The Vatican City are de facto participants in the Schengen Area.
Put into context, the Schengen Area acts like a single entry and exit point for international travel. If a third-country national were to enter the Schengen area from Germany, they would be free to travel within all other Schengen countries for 90 days during any 180 days. They need not go through any border checks.
Once those 90 days are up, an applicant would need to wait 90 days before applying for another Schengen visa.
The traveller would be free to leave from another Schengen Treaty signatory country such as Italy or Spain and would then be subject to an exit border check-in that state.
When the migrant crisis was at its peak in 2016, border controls were temporarily put back into effect in seven Schengen area countries: Austria, Denmark, France, Germany, Norway, Poland, and Sweden.
EU members are now obliged to join the Schengen Area as soon as they fulfil the technical and legal requirements and obligations attached to it.