Article 49 of the Treaty on EU stipulates that any European country that respects values enlisted in the Article 2 and is devoted to promoting them can submit candidacy for joining EU. European Parliament as well as national parliaments are informed on candidacy. Country submitting the candidacy consigns it to the Council, who decides unanimously and after the consultations with the Commission and approval of the European Parliament (who decides by majority of its members).
Currently candidate countries are:
Potential candidates are Albania, Bosnia and Herzegovina and Kosovo according to the UNSCR 1244.