The Treaty of Lisbon, also known as the Lisbon Treaty, is an international treaty which amends the Treaty on European Union and the Treaty Establishing the European Community. The Lisbon Treaty was signed by the heads of state and government of the 27 EU Member States on 13 December 2007 in Lisbon. The Republic of Croatia accepted the Lisbon Treaty during the EU accession process as the 28th Member State. The Lisbon Treaty entered into force only after the correction of the Irish referendum, on 1 December 2009. The Lisbon Treaty amends the existing Treaties on European Union and the European Community, without replacing them. Among the changes introduced by the Lisbon Treaty, particular emphasis should be put on those relating to strengthening of the position and role of the European Union institutions. With receiving the new Member States, the European Union has grown and has had to deal with numerous changes such as climate changes, global recession and international cross-border crime. In order to be able to function effectively, the European Union needed a system that would improve the way it works. That is the purpose of the Lisbon Treaty which makes the European Union more democratic, more efficient and more transparent. The right of a Member State to withdraw from the European Union was for the first time introduced with the Lisbon Treaty.