With the Treaty of Lisbon, codecision officially became the 'Ordinary Legislative Procedure' (Article 294 TFEU) and the general rule for adopting legislation at European Union level, covering the vast majority of areas of Union action. The Ordinary Legislative Procedure is based on the principle of parity between the directly elected European Parliament, representing the people of the Union, and the Council, representing the governments of Member States. On the basis of a proposal by the Commission, the two co-legislators adopt legislation jointly, having equal rights and obligations. A Joint Declaration of the Parliament, the Council and the Commission, agreed in 1999 and revised in 2007, lays down practical arrangements on the operation of the procedure.
Maastricht Treaty, November 1993: First introduction of the codecision procedure which covered a limited number of legislative areas (mainly internal market).
Amsterdam Treaty, May 1999: Simplification of the codecision procedure making it possible to conclude agreements at first reading. Extension of its scope to more than 40 legal bases (including transport, environment, justice and home affairs, employment and social affairs).
Nice Treaty, February 2003: Extension of the scope of the codecision procedure to further areas.
Lisbon Treaty, December 2009: Codecision officially becomes the Ordinary Legislative Procedure, covering 85 areas of Union action (including agriculture, fisheries and common commercial policy).