For the last 15 years, Europe has gone through a piecemeal process of becoming a continent without internal borders. On March 26, 1995, the Schengen Agreement took effect, after being signed by five central EU members Belgium, France, Germany, Luxembourg and the Netherlands.
Since then, the visa-free Schengen area has grown to include all other members of the EU, with the exception of Great Britain and Ireland - who chose not to join - and the relatively new members Bulgaria, Cyprus and Romania.
Apart from the 22 participating EU member states, the Schengen area also includes the non-members Iceland, Norway and Switzerland. The Swiss were the last to join - at the end of 2008.
With the exception of random police checks at airports, train stations and on highways, border controls between Schengen states no longer exist.
But Schengen isn't just about making travel easier.
One of the most important - and overlooked - aspects of the agreement is its effect on European integration, according to Daniela Kietz of the German Institute for Foreign Affairs and Security Policy.
"Lifting internal borders has made EU-wide measures in areas like migration, asylum, and police cooperation absolutely necessary," Kietz said. "For example, after the agreement took effect, Schengen member states couldn't control migration or asylum flows into their countries anymore. In order to balance this, EU-wide measures as part of an all-encompassing migration policy had to be installed."
Schengen has, however, also greatly complicated the issue of migration in the bloc, according to Kietz.
"Germany and all other member states can no longer control who enters their territories, be it legally or illegally. Illegal immigrants who enter the Schengen area can obviously move freely within the EU, and this has led to the phenomenon of 'asylum shopping.' "
Once in the EU, "asylum shoppers" seek out the countries that offer the highest standard of living - or where they think their chances of being granted asylum are better. That has led to some EU member states having to deal with higher asylum burdens than others, Kietz said.
One of the biggest fears associated with the visa-free zone, especially as it expanded, was that security would be compromised and crime rates would spike.
Yet, none of the Schengen states reported major increases in crime after dismantling their border controls.
Kietz said that was due in large part to the fact that police forces of the Schengen states have been cooperating closely for more than a decade.
"Germany, for example, has police cooperation agreements with all other member states in order to efficiently work together so as not to leave any member state by itself."
Implementing Schengen has indeed been one of the central goals of European internal affairs. It's also one that Europe believes it has mastered, according to European Commission spokesman Michele Cercone.
"The challenges were there from the beginning, and I have to say that 15 years later we can clearly say that this has been quite a successful story," Cercone said.
Author: Gabriel Borrud
Editor: Nancy Isenson