High Quality Content by WIKIPEDIA articles! The Treaty of Lisbon or Lisbon Treaty (initially known as the Reform Treaty) is an international agreement that amends the two treaties which comprise the constitutional basis of the European Union (EU). The Lisbon Treaty was signed by the EU member states on 13 December 2007, and entered into force on 1 December 2009. It amends the Treaty on European Union (TEU; also known as the Maastricht Treaty) and the Treaty establishing the European Community (TEC; also known as the Treaty of Rome). In this process, the Rome Treaty was renamed to the Treaty on the Functioning of the European Union (TFEU).