It has been a long journey to reach the current number of members states:
- 1952: Germany, Belgium, France, Italy, Luxembourg and Netherlands
- 1973: Denmark, Ireland and United Kingdom (left on 31 January 2020)
- 1981: Greece
- 1986: Spain and Portugal
- 1995: Austria, Finland and Sweden
- 2004: Cyprus, Slovenia, Slovakia, Estonia, Hungria, Latvia, Lithuania, Malta, Poland and Czech Republic
- 2007: Bulgaria and Romania
- 2013: Croatia
- Candidate countries: Albania, Bosnia and Herzegovina, Moldova, Montenegro, North Macedonia, Serbia, Türkiye and Ukraine
Leyenda