Opt-outs in the European Union in the context of "Enhanced cooperation"

The Schengen Area (English: /ˈʃɛŋən/ SHENG-ən, Luxembourgish: [ˈʃæŋən] ) is a system of open borders that encompass 29 European countries that have officially abolished border controls at their common borders. As an element within the wider area of freedom, security and justice (AFSJ) policy of the European Union (EU), it mostly functions as a single jurisdiction under a common visa policy for international travel purposes. The area is named after the 1985 Schengen Agreement and the 1990 Schengen Convention, both signed in Schengen, Luxembourg.

Of the 27 EU member states, only two are not members of the Schengen Area. Cyprus is committed by treaty to join the system and aims to do so by 2026, although its participation has been complicated by the occupation of Northern Cyprus by Turkey since 1974. Ireland maintains an opt-out and operates its own visa policy.

Denmark holds opt-outs from European Union policies in relation to police and justice and the adoption of the euro. They were secured under the Edinburgh Agreement in 1992 after a referendum for the ratification of the Maastricht Treaty was rejected by Danish voters, as a package of measures to assuage concerns raised during that referendum.

The Danish government has held three referendums on modifying its opt-outs. The first in 2000 rejected the adoption of the euro by 53.2% to 46.8% on a turnout of 87.6%. The second in 2015 rejected converting Denmark's current full opt-out on home and justice matters into a case-by-case opt-out similar to that held by Ireland and the United Kingdom (the latter until its exit from the EU) by 53.1% to 46.9%. The third in 2022 abolished the defence opt-out with 66.9% voting yes, and 33.1% voting no.

The United Kingdom was a member state of the European Union and of its predecessor the European Communities from 1973 until 2020. Since the foundation of the European Communities, it has been an important neighbour, and was a leading member state until its withdrawal from the EU on 31 January 2020 as a result of Brexit, ending 47 years of membership.

In general, the law of the European Union is valid in all of the European Union member states. However, occasionally member states negotiate certain opt-outs from legislation or treaties of the European Union, meaning they do not have to participate in certain policy areas. The United Kingdom had four opt-outs in place before leaving the Union–the most of any EU member state, making it the least integrated member state.

A referendum on one of the country's opt-outs from the European Union was held in Denmark on 3 December 2015. Specifically, the referendum was on whether to convert Denmark's current full opt-out on home and justice matters into an opt-out with case-by-case opt-in similar to those held by Ireland and the United Kingdom. Approval of the referendum was needed for Denmark to remain in Europol under the new rules. However, it was rejected by 53% of voters.

A referendum on the abolition of the defence opt-out, one of the country's opt-outs from the European Union, was held in Denmark on 1 June 2022. The referendum was announced on 6 March 2022 following a broad multi-party defence agreement reached during the 2022 Russian invasion of Ukraine. The referendum was approved with the "Yes" side securing approximately two-thirds of the vote.