This chapter, which traces the chronological history of the development of the European Economic Community (EEC) into the European Union (EU), explains that the EEC was created by the Treaty of Rome (ToR) in 1957 and discusses Treaties which amended the ToR and led to the development of the EU. These include the Single European Act in 1987, the Maastricht Treaty in 1993, the Amsterdam Treaty in 1999, the Nice Treaty in 2003 and the Lisbon Treaty in 2009. The chapter also describes the nature of the EU and theories explaining the development of the scope of its activities. It summarises the history of the EU, including enlargement, debates over democracy, and the Brexit process, and explains the nature of the EU: supranational, intergovernmental or a form of ‘multilevel governance’?