Türkiye joined as CERN’s first Associate Member State.

On 16 May 2025, CERN Director-General Fabiola Gianotti and Minister of Science, Technology, Knowledge and Innovation of Chile, Aisén Etcheverry signed an agreement admitting Chile as an Associate Member State of CERN

Brazil has become the first Associate Member State of CERN in the Americas

On 8 May 2025, CERN Director-General Fabiola Gianotti and Irish Minister for Further and Higher Education, Research, Innovation and Science James Lawless signed an agreement admitting Ireland as an Associate Member State of CERN

The Estonian flag was raised at a ceremony held at CERN to mark the country’s accession as CERN’s 24th Member State.

From CERN press release dated 24 March 2019: Today, CERN welcomes Serbia as its 23rd Member State, following receipt of formal notification from UNESCO that Serbia has acceded to the CERN Convention. When Serbia was a part of Yugoslavia, which was one of the 12 founding Member States of CERN in 1954, Serbian physicists and engineers took part in some of CERN’s earliest projects, at the SC, PS and SPS facilities. In the 1980s and 1990s, physicists from Serbia worked on the DELPHI experiment at CERN’s LEP collider. In 2001, CERN and Serbia concluded an International Cooperation Agreement, leading to Serbia’s participation in the ATLAS and CMS experiments at the Large Hadron Collider, in the Worldwide LHC Computing Grid, as well as in the ACE and NA61 experiments. Serbia’s main involvement with CERN today is in the ATLAS and CMS experiments, in the ISOLDE facility, which carries out research ranging from nuclear physics to astrophysics, and on design studies for future particle colliders – FCC and CLIC – both of which are potentially new flagship projects at CERN. Read the press release here.

From CERN press release dated 17 July 2016:

On 17 July 2016, Romania became the twenty-second Member State of CERN.

Contacts between CERN and Romania began back in 1991, when a scientific and technical cooperation agreement was signed, establishing the legal framework for later developments.

Aspiring to become a full-fledged Member State and thus to contribute fully also to the governance of the Laboratory, Romania submitted its formal application to join the Organization in April 2008. The Agreement granting Romania the status of Candidate for Accession came into force on 12 November 2010.

Romania's scientific community at CERN has grown over the years and currently numbers around a hundred visiting scientists. Romania has particularly strong presence in the LHC experiments ATLAS, ALICE and LHCb. Romanian researchers and engineers also work at DIRAC and n_TOF at the Proton Synchrotron (PS), on the NA62 experiment at the Super Proton Synchrotron (SPS), and at the ISOLDE facility. Romania is also active in the Worldwide LHC Computing Grid.

Read the press release here.

From CERN press release dated 15 January 2014: 

At a ceremony today at CERN, the Israeli flag was hoisted for the first time to join the other 20 flags of the organization’s Member States, after UNESCO officially recorded Israel's accession as a new CERN Member State on 6 January 2014.

Following the ceremony, Mr Avigdor Liberman, Deputy Prime Minister and Minister of Foreign Affairs of the State of Israel, visited the LHC tunnel and the ATLAS experiment, accompanied by a delegation of officials and representatives of the Israeli scientific community.

"In my visit in CERN today, I have witnessed the frontiers of science. I have realized the scope of collaboration between Israel and CERN. Israeli scientists and their CERN colleagues share a dedication to scientific excellence, technological development and education. Israel and CERN share ideals and goals and therefore have a wide prospect for cooperation," said Mr Avigdor Liberman.

"I am very honoured as Director-General to welcome Israel as a new Member State. CERN and Israel have already a long history of mutual collaboration, and this day will undoubtedly be memorable, promising increasingly fruitful scientific cooperation between CERN and the Israeli physics community," said CERN’s Director-General Rolf Heuer.

On 29 September 1961, the Federal Republic of Yugoslavia gave formal notice to CERN of its intention to withdraw from the organization at the end of the year, after Yugoslavia struggled to pay its yearly contributions. This formal notice confirmed an informal advance notice given on 19 May, by a letter that was circulated to the CERN council.

At the request of the Spanish government, Spanish contributions to the CERN budget for 1964, 1965 and 1966 were reduced by 50%, 35% and 20% respectively. In a letter on 21 September 1966 to the Director-General the government asked for a further reduction of 35% from 1967 onwards. The CERN finance committee rejected the request.

Minutes of the CERN council, 19-20 June, 1969:

At the 40th Session of council last year, Spain asked that her notice of withdrawal from the organization contained in her letters of 8 August and 30 October should be held in suspense whilst her authorities studied further the possibility of her remaining in CERN.

By letter of 2 June 1969, Spain notified the Director-General that no solution had been found possible and that consequently her withdrawal from the organization would take effect as from 31 December 1968.

The council is now invited to take note of the withdrawal of Spain from the organization.

Spain formally withdrew from CERN on 31 December 1968.