Accession of new Member States to the European Union (EU) is governed by Article 49 of the EU Treaty. A state that wishes to become a member of the Union must satisfy two conditions:

• it must be a European state;
• it must respect the common values of the Member States and undertake to promote them. These are human dignity, liberty, democracy, the rule of law, and respect for human rights including minorities (Article 2 of the EU Treaty).

The conditions and date of accession, any transition periods required and the adjustments to the Treaties on which the Union is founded must be agreed in the form of an accession treaty between the candidate country and the Member States.

To give due form to the accession, this treaty is ratified by all the Member States and the candidate country in accordance with their own constitutional rules.

In practice, accession is not automatic, since it depends on the situation of the candidate country concerned. There is thus a pre-accession period of varying length, during which the candidate countries adapt their institutions, standards and infrastructure to enable them to meet their obligations as Member States at the time of accession.