The Schengen Agreement comprises two different agreements which were ratified in 1985 and 1990 respectively. Together, they abolished border controls and greatly facilitated transit through Europe. The two individual agreements stipulated: Originally, the Schengen Treaties and subsequent rules were officially independent of the EEC and its successor, the European Union (EU). In 1999, they were incorporated into European Union law by the Treaty of Amsterdam, which codified Schengen in EU law while providing opt-outs for Ireland and the United Kingdom, the latter providing for opt-outs since their exit from the EU. EU Member States that do not have an opt-out and have not yet joined the Schengen area are legally obliged to do so if they meet the technical requirements. Although it is linked to EU law, several third countries that have signed the agreement are included in the territory. Now that the Schengen Agreement is part of the acquis communautaire, it has lost treaty status for EU members, which could only be changed on its terms. Instead, changes are made in accordance with the EU legislative process under the EU Treaties.  Ratification by the former signatories of the Convention is not necessary to amend or repeal all or part of the old Schengen acquis.  Acts laying down the conditions for accession to the Schengen area are now adopted by a majority of EU legislative bodies.
The new EU Member States do not sign the Schengen Agreement as such, but are required to implement the Schengen rules within the framework of existing EU law, which any new entrant must accept. [Citation required] The United Kingdom and Ireland have participated in certain aspects of the Schengen Agreement, such as the Schengen Information System (SIS), since 2000 and 2002 respectively. The ETIAS travel authorisation gives access to all the countries included in the Schengen Agreement, i.e. the ETIAS and Schengen countries are identical, an ETIAS authorisation is effectively a Schengen visa. Differences of opinion between Member States led to an impasse in the abolition of border controls within the Community, but in 1985 five of the then ten Member States – Belgium, France, Luxembourg, the Netherlands and West Germany – signed an agreement on the phasing out of common border controls. .