The EU has developed an internal single market through a standardised system of laws that apply in all member states. EU policies aim to ensure the free movement of people, goods, services, and capital within the internal market, enact legislation in justice and home affairs, and maintain common policies on trade, agriculture, fisheries, and regional development. Within the Schengen Area, passport controls have been abolished. A monetary union was established in 1999 and came into full force in 2002, and is composed of 19 EU member states which use the euro currency.
The EU operates through a hybrid system of supranational and intergovernmental decision-making. The seven principal decision-making bodies—known as the institutions of the European Union—are the European Council, the Council of the European Union, the European Parliament, the European Commission, the Court of Justice of the European Union, the European Central Bank, and the European Court of Auditors.
The EU traces its origins from the European Coal and Steel Community (ECSC) and the European Economic Community (EEC), formed by the Inner Six countries in 1951 and 1958, respectively. The community and its successors have grown in size by the accession of new member states and in power by the addition of policy areas to its remit. The
Covering 7.3% of the world population, the EU in 2014 generated a nominal gross domestic product (GDP) of 18.495 trillion US dollars, constituting approximately 24% of global nominal GDP and 17% when measured in terms of purchasing power parity. Additionally, 26 out of 28 EU countries have a very high Human Development Index, according to the United Nations Development Program. In 2012, the EU was awarded the Nobel Peace Prize. Through the Common Foreign and Security Policy, the EU has developed a role in external relations and defence. The union maintains permanent diplomatic missions throughout the world and represents itself at the United Nations, the World Trade Organization, the G8, and the G-20. Because of its global influence, the European Union has been described as a current or as a potential superpower.
In order to start the process to leave the EU, the British government will have to invoke Article 50 of the Treaty on European Union. There is a dispute whether under the Scotland Act 1998, the Scottish Parliament has to consent to measures that eliminate EU laws' application in
Membership of the EU and its predecessors was a topic of debate in the United Kingdom before the country joined the European Economic Community (EEC, or "Common Market") in 1973, and subsequently. In accordance with a Conservative Party manifesto commitment, the legal basis for a referendum was established by the UK Parliament through the European Union Referendum Act 2015. It was the second time the British electorate had been asked to vote on the issue of the