The CERN Convention was signed in 1953 by the twelve founding states Belgium, Denmark, France, the Federal Republic of Germany, Greece, Italy, the Netherlands, Norway, Sweden, Switzerland, the United Kingdom and Yugoslavia, and entered into force on September 29, 1954. The Organization was subsequently joined by Austria (1959), Spain (1961-1969, re-joined 1983), Portugal (1985), Finland (1991), Poland (1991), CzechoSlovak Republic (1992), Hungary (1992), Bulgaria (1999) and Israel (2014). The Czech Republic and Slovak Republic re-joined CERN after their mutual independence in 1993. Yugoslavia left CERN in 1961. Thus, CERN today has 21 Member States.
All Member States are represented in the CERN Council, the supreme governing body of the Organization. The International Relations Office coordinates all day-to-day relations between the CERN Management and the Member States. Administrative relations with the two host states France and Switzerland are under the responsibility of the Relations with the Host States Service.