Definition of Lisbon treaty
The EU’s Lisbon treaty on institutional reform was signed in the Portuguese capital in 2007. The treaty aims to simplify and modernise the EU’s institutions, following the bloc’s enlargement from 15 to 27 member states since April 2004.
It creates a semi-permanent president of the European Council (representing national governments) and guarantees each member state one seat on the European Commission. It also enhances the role of the European Parliament and national parliaments and changes the EU’s voting procedures.
The treaty came into effect on 1 December 2009. 
From 2010, the treaty gives the EU authority to take action in the eurozone (Article 136), on which basis many reforms are being made.