An EU States’ land borders, including river and lake borders, sea borders and their airports, river ports, sea ports and lake ports, provided that they are not internal borders.
With the signing on 14 June 1985 of the Schengen Agreement, Belgium, France, Germany, Luxembourg and the Netherlands agreed that they would gradually remove controls at their common borders and introduce freedom of movement for all nationals of the signatory EU States, other EU States or non-EU countries. The Schengen Convention, signed on 19 June 1990, supplements the Agreement and lays down the arrangements and safeguards for implementing freedom of movement.
The Agreement and the Convention, the rules adopted on the basis thereof and the related agreements together form the "Schengen acquis". Since 1999, this has formed part of the institutional and legal framework of the EU by virtue of a Protocol to the Treaty of Amsterdam.