Brexit is the withdrawal of the United Kingdom (UK) from the European Union (EU) and the European Atomic Energy Community on 31 January 2020. The UK is to date the first and only country to formally leave the EU after 47 years of membership and cautious integration within the bloc after it first joined its predecessor the European Communities (EC) on 1 January 1973. It is also thought to be the first country to voluntarily withdraw from an economic and monetary union of countries. Currently it continues to participate in the European Union Customs Union and European Single Market during a transition period that will end on 31 December 2020.