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