The Treaty to establish a Constitution for Europe was agreed by the Heads of State and Government of the European Union's twenty-five Member States on 18 June 2004. The agreement was followed by a signing in Rome on 29 October 2004. This is not the final step however: all the member states of the EU now have to ratify the Constitution according to the national procedures. In some cases this will be done through referendum in other through parliamentary approval.

The Constitution is intended to replace all existing EU Treaties with a single consolidated document. During the process of drafting the Constitution, all the previous Treaties have been amended and merged into a single document. The main purpose is to simplify the understanding of the Union's legal basis.

The European Constitution is the outcome of a lengthy process of debate and negotiation. It aims to clarify the nature of the European Union, the extent of its powers and its relationship with its Member States.

While in most policy areas it does not significantly alter the Union's existing role, it does contain important innovations in several areas. These include the protection of fundamental rights, combating cross-border crime, the role of national parliaments in EU affairs, voting in the EU Council, and the conduct of the Union's foreign policy.

The European Constitution is a relatively large document and consists of four main parts:

• Part I (pdf) covers the definition and objectives of the Union, fundamental rights and citizenship of the Union, the Union's competences and how they are exercised, its institutions, the democratic life of the Union, the Union's finances, its immediate environment, and membership of the Union.
• Part II of the Constitution (pdf) contains the Charter of Fundamental Rights.
• Part III (pdf) sets out in detail the Union's policy areas and other technical issues,
• Part IV (pdf) deals with the Treaty establishing the European Constitution, including arrangements for ratification and future amendments.
• In addition, several Protocols and Declarations (pdf) are attached to the European Constitution, many of them carried over from previous Treaties.