There are two broad types of agency, each with different characteristics and raising different issues.
On 26 March 1995 the abolition of border controls between Belgium, Germany, Spain, France, Luxembourg, the Netherlands and Portugal became reality.
Today we are celebrating the 20th anniversary of the entry into force of the Schengen Convention which made it possible for citizens to travel freely to visit friends and family, make business trips or visit other Schengen countries as tourists, without giving up on security.
Since then, more countries have joined and the Schengen area currently consists of 26 countries, including four non-EU countries.
"This year we are celebrating 30 years of Schengen, but also 20 years of the abolishment of internal border controls. Europeans make over 1.25 billion journeys within the Schengen area every year. A Europe without internal borders brings huge benefits to the economy as well, which shows how tangible, popular and successful the Schengen achievement is and the importance it has for our daily lives and for our societies. We need to preserve and reinforce this common achievement. The creation of the Schengen area is one of the greatest achievements of the EU, and it is irreversible", said Dimitris Avramopoulos, Commissioner for Migration, Home Affairs and Citizenship