1975 United Kingdom European Communities membership referendum in the context of "United Kingdom–European Union relations"

This is a list of referendums related to the European Union, or referendums related to the European Communities, which were predecessors of the European Union. Since 1972, a total of 48 referendums have been held by EU member states, candidate states, and their territories, with several additional referendums held in countries outside the EU. The referendums have been held most commonly on the subject of whether to become a member of European Union as part of the accession process, although the EU does not require any candidate country to hold a referendum to approve membership or as part of treaty ratification. Other EU-related referendums have been held on the adoption of the euro and on participation in other EU-related policies.

The United Kingdom is the only country as an EU member state to have held referendums on continued membership of the European Union and its antecedent organisation, the European Communities. In the first referendum in 1975, continued membership of what was then the European Communities (which included the European Economic Community, often referred to as the Common Market in the UK) was approved by 67.2% of voters, while in its second referendum in 2016 voters voted by 51.9% to leave the European Union, effectively reversing the result of the first referendum.

The 2016 United Kingdom European Union membership referendum, commonly referred to as the EU referendum or the Brexit referendum, was a referendum that took place on 23 June 2016 in the United Kingdom (UK) and Gibraltar under the provisions of the European Union Referendum Act 2015 to ask the electorate whether the country should continue to remain a member of, or leave, the European Union (EU). The result was a vote in favour of leaving the EU, triggering calls to begin the process of the country's withdrawal from the EU commonly termed "Brexit".

Since 1973, the UK had been a member state of the EU and its predecessor the European Communities (principally the European Economic Community), along with other international bodies. The constitutional implications of membership for the UK became a topic of debate domestically particularly regarding sovereignty. A referendum on continued membership of the European Communities (EC) to try and settle the issue was held in 1975, with 67% of voters approving continued membership. Between 1975 and 2016 as European integration deepened, subsequent EC/EU treaties and agreements were ratified by the UK Parliament but without any public approval. Following the Conservative Party's victory at the 2015 general election as a main manifesto pledge, the legal basis for the EU referendum was established through the European Union Referendum Act 2015. Prime Minister David Cameron also oversaw a renegotiation of the terms of EU membership, intending to implement these changes in the event of a Remain result. The referendum was legally non-binding due to the ancient principle of parliamentary sovereignty, although the government promised to implement the result.

The 2016 United Kingdom European Union membership referendum took place in the United Kingdom and Gibraltar on 23 June 2016. Membership of the European Union had been a topic of political debate in the United Kingdom since the country joined the European Communities (then commonly referred to as the "Common Market" by the British people) in 1973. This referendum was conducted very differently from the European Communities membership referendum in 1975; a more localised and regionalised counting procedure was used, and the ballot was overseen by the Electoral Commission, a public body that did not exist at the time of the first vote. This article lists, by voting area for Great Britain and Gibraltar and by parliamentary constituency for Northern Ireland, all the results of the referendum, each ordered into national and regional sections.

Under the provisions of the European Union Referendum Act 2015, there were a total of 382 voting areas across twelve regions, using the same boundaries as used in European Parliamentary elections since 1999, under the provisions of the European Parliamentary Elections Act 2002, with votes counted at local authority level. In England the 326 local government districts were used as the voting areas; these consist of all unitary authorities, all metropolitan boroughs, all shire districts, the London boroughs, the City of London and the Isles of Scilly. The nine regions of England were then also used to count the votes at the regional level, with Gibraltar being regarded as part of South West England. Northern Ireland was a single voting area as well as being a regional count, although local totals by Westminster parliamentary constituency area were announced. In Scotland the 32 Scottish council areas were used as voting areas, and there was a single national count. In Wales the 22 Welsh council areas were used as the voting areas, and there was a single national count.