Following the establishment of the European Coal and Steel Community (ECSC) by Belgium, France, Germany, Italy, Luxembourg and Netherlands in 1951 the Union has been enlarged on the following occasions:
| Denmark | Ireland | United Kingdom |
| Greece |
| Portugal | Spain |
| Austria | Finland | Sweden |
| Czech Republic | Cyprus | Estonia |
| Hungary | Latvia | Lithuania |
| Malta | Poland | Slovakia |
| Slovenia |
Expected accession of
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| Bulgaria | Romania |