The Treaty of Lisbon (initially known as the Reform Treaty) is an international agreement that amends the two treaties which form the constitutional basis of the European Union (EU). The Treaty of Lisbon, which was signed by the EU member states on 13 December 2007, entered into force on 1 December 2009. It amends the Maastricht Treaty (1992), known in updated form as the Treaty on European Union (2007) or TEU, as well as the Treaty of Rome (1957), known in updated form as the Treaty on the Functioning of the European Union (2007) or TFEU. It also amends the attached treaty protocols as well as the Treaty establishing the European Atomic Energy Community (EURATOM).