EU leaders will meet in Lisbon, Portugal to sign a landmark treaty that will change the way the union members govern themselves. The document the leaders of the 27 countries will sign is the European Union Reform Treaty, which will replace the current unsuccessful EU constitution.

If adopted, the new treaty will create an EU president and a more powerful foreign policy chief. The main stated intention of the “new deal” is to improve the bloc's ability to act together as it grows.

This new constitution follows the French and Dutch opposition that led to the current one’s abandon. EU leaders underlined the fact that the texts of the two constitutions are nothing alike.

Nevertheless, the new treaty includes some of the draft constitution's main reforms, thus putting several governments under domestic pressure.  

This original text of the Union’s first constitution was signed in 2004, when it gave the EU its official anthem (Beethoven's "Ode to Joy"), a foreign minister and a charter of rights comparable to the U.S. Bill of Rights.

That first EU constitution, which has included all the treaties and legislation, led to the transformation of the EU from a minimalist trading bloc of six countries, into a political and economic union of 27 members. However, the draft constitution has encountered stiff opposition in referendums, especially in France and the Netherlands in 2005 and it was never ratified.

The new version of the constitution it is no longer called a constitution, it has no anthem or flag mentioned in it and it’s much shorter and contains several opt outs for the  countries that oppose further EU integration.

Only Ireland will hold a referendum to ratify the treaty, thus the adoption of the new treaty is very probable and will take place next year. However, the treaty remains very controversial.

The current system – in which member states take turns to hold the EU presidency for six months - will be replaced by an EU president that will serve a five-year term.

British Prime Minister Gordon Brown is the only one of the 27 EU leaders that is not sure to sign the treaty. He is expected to arrive at the place where the meeting is held - Lisbon's Jeronimos Monastery – and sign the document.

EU leaders are to meet again in Brussels on Friday for a traditional end-of-year summit.