The Treaty of Lisbon (initially known as the Reform Treaty) is an international agreement which amends the two treaties which form the constitutional basis of the European Union (EU). The Treaty of Lisbon was signed by the EU member states on 13 December 2007, and entered into force on 1 December 2009. It amends the Maastricht Treaty (1993), also known as the Treaty on European Union, and the Treaty of Rome (1958), also known as the Treaty establishing the European Community (TEEC). The Treaty of Lisbon, renamed the Treaty of Rome to the Treaty on the Functioning of the European Union (TFEU).