Since 1999, the Schengen acquis (rule of law) has been integrated into the legal framework of the European Union. The essential provisions of the Schengen border code established by Regulation 562/2006 are the removal of internal borders between Schengen countries and the parallel reinforcement of the external borders of the Schengen area. The removal of internal borders guarantees the free movement of EU citizens and qualified third-country nationals. Third-country nationals are subject to extensive monitoring at the entrance and exit of the Schengen area, while EU citizens and others who play the right to free movement are subject to minimum screening for identity purposes. One of the key features of the Schengen area is the Schengen Information System (SIS), a large database used by the national authorities responsible for maintaining public security in the Schengen area and effectively managing external borders. Participating countries are primarily responsible for the management of their external borders, while being allowed to enter into bilateral agreements with neighbouring countries for the implementation of a local border regime. In addition, Schengen countries retain the right to re-establish internal controls for a period of six months in exceptional cases.  Id. Art. 2, par. 5, letter a), b. The free movement of persons is extended to citizens of the European Economic Area (EEA) on the basis of an agreement with Norway, Iceland and Lichtenstein, as well as to Swiss citizens.
 Schengen Information System (SIS), European Commission, Home Affairs, ec.europa.eu/dgs/home-affairs/what-we-do/policies/borders-and-visas/schengen-information-system/index_en.htm (last updated 31 August 2012). The Schengen area first included Germany, France, Luxembourg, Belgium and the Netherlands. The first agreement was signed on 14 June 1985 and was followed by an implementation agreement in 1990. They came into force in 1995 and were transposed into EU law in May 1999 by the Treaty of Amsterdam. Most EU Member States are therefore bound by the Schengen acquis, with the exception of the OPT-out clauses of the United Kingdom and Ireland: Ireland only participates in the Schengen Information System (SIS), while the United Kingdom also participates in judicial and criminal cooperation. With regard to Cyprus, Romania and Bulgaria, implementation is suspended until the European Council decides that the conditions for the abolition of internal borders are fully met.