| Member States | |
|---|---|
| Dates of Accession | |
| Austria | 1 June 1959 |
| Belgium | 1953 |
| Bulgaria | 11 March 1999 |
| Czech Republic | 1 July 1993 |
| Denmark | 1953 |
| Estonia | 30 August 2024 |
| Finland | 1 January 1991 |
| France | 1953 |
| Germany | 1953 |
| Greece | 1953 |
| Hungary | 1 July 1992 |
| Israel | 6 January 2014 |
| Italy | 1953 |
| Netherlands | 1953 |
| Norway | 1953 |
| Poland | 1 July 1991 |
| Portugal | 1 January 1986 |
| Romania | 17 July 2016 |
| Serbia | 24 March 2019 |
| Slovakia | 1 July 1993 |
| Spain | 1 January 1961 to 31 December 1968 and from 1 January 1983 |
| Sweden | 1953 |
| Switzerland | 1953 |
| United-Kingdom | 1953 |
| Associate Member States in the pre-stage to Membership | |
|---|---|
| Cyprus | 1 April 2016 |
| Slovenia | 4 July 2017 |
| Associate Member States | |
|---|---|
| Brazil | 13 March 2024 |
| Croatia | 10 October 2019 |
| India | 16 January 2017 |
| Latvia | 2 August 2021 |
| Lithuania | 8 January 2018 |
| Pakistan | 31 July 2015 |
| Turkey | 6 May 2015 |
| Ukraine | 5 October 2016 |
| Observers | |
|---|---|
| European Union | 1 July 1985 |
| JINR | 18 September 2014 --Status suspended as from 25 March 2022-- |
| UNESCO | 1 July 1955 |
| Japan | 1 July 1995 |
| Russian Federation | 1 July 1991 --Status suspended as from 8 March 2022-- |
| U.S.A. | 1 July 1998 |