European Commission - Enlargement - Treaty of accession
The treaty of accession is signed by the member states and the acceding country* once accession negotiations* have come to a close. Accession is not however automatic as the Treaty has to be ratified by the Member States and the acceding country. The Treaty enters into force after ratification on a date that has been previously determined, setting out the conditions and arrangements regarding accession, including the rights and obligations of the new Member State as well as adaptations to the EU institutions.
For more details, see the following sections on our website: