On Saturday 20th February 2015, David Cameron announced that the UK's In/Out referendum on the European Union would take place on 23rd June 2016.
Here are the key events leading up to and beyond this date.
1950 – 'The Schuman Declaration'. French Foreign Minister Robert Schuman presented a plan for cooperation between European states.
1957 – Belgium, France, Italy, Luxembourg, the Netherlands and West Germany sign the Treaty of Rome, which launches the European Economic Council (EEC).
1963 – Charles de Gaulle vetoes UK entry.
1973 – Accession of Denmark, Ireland and the UK.
1975 – UK Referendum on continued membership of the EEC.
1979 – First direct elections to Parliament.
1981 – Accession of Greece.
1985 – Delors Commission; Greenland leaves Community.
1986 – Single European Act; Accession of Portugal and Spain; flag adopted.
1989 – The Iron Curtain fell creating an opportunity to unify Europe. This led to the reunification of Germany on 3rd October 1990.
1992 – Maastricht Treaty formally called the Treaty on European Union. The European Union is born and the Euro was introduced (Denmark and the UK are not included in the European Monetary Union (EMU)).
1995 – Accession of Austria, Finland and Sweden.
2002 – Euro notes and coins came into circulation in a number of Member States as national currencies were phased out.
2004 – Accession of ten countries (Cyprus, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia).
2007 – Accession of Bulgaria and Romania.
2009 – The Lisbon Treaty came into force with the aim of strengthening the EU's ability to act on the global stage, and give a greater voice to the European Parliament, national parliaments and citizens.
2013 – Accession of Croatia.
2013 – (22nd January) UK Prime Minister David Cameron confirms that if the Conservatives win the next election, the UK's relationship with the EU would be renegotiated.
2015 – (7th May) The Conservative Party gains an overall majority in the general election.
2015 – (27th May) The European Union Referendum Bill was announced in the Queen's Speech, which is required to allow the referendum to take place.
2015 – (1st September) Headed by British official Jonathan Faull, a new group charged with handling issues relating to the EU referendum began its work. It reports to European Commission President Jean-Claude Juncker.
2016 – (18th-19th February) David Cameron gets the 27 other EU member state to sign up to a package of reforms at EU summit.
2016 – (20th February) Referendum date is announced.
2016 – (March/April) Secondary legislation is due to be laid before Parliament paving the way for a referendum. The Electoral Commission will designate the official Leave and Remain campaigns, which will get access to public funds, a £7m spending limit and TV broadcasts.
2016 – (5th May) Elections to devolved parliaments in Scotland, Wales and Northern Ireland to take place. Elections will also take place for English local authorities and for London's mayor.
2016 – (23rd June) Referendum – "Should the United Kingdom remain a member of the European Union or leave the European Union?"
2016 – (23rd June) The United Kingdom votes to leave the European Union by 52% to 48%.
2016 – (24th June) David Cameron resigns as Prime Minister.
2016 – (11th July) Theresa May becomes leader of the Convervative Party.
2016 – (9th October) Prime Minister Thereas May announced she would trigger Article 50 by the end of March 2017.
2017 onwards – In the event of a Leave vote, a country can withdraw from the EU two years afterof its intention to leave. However, leaving would still involve "complex and probably lengthy negotiations".