CERN is the European Organization for Particle Physics Research, the world's largest particle physics laboratory, situated on the border between France and Switzerland, just west of Geneva. The convention establishing it was signed on September 29, 1954. From the original 12 signatories of the CERN convention, membership has grown to the present 20 Member States.
The acronym originally stood, in French, for Conseil Européen pour la Recherche Nucléaire (European Council for Nuclear Research), which was a provisional council for setting up the laboratory, established by 11 European governments in 1952. The acronym was retained  for the new laboratory after the provisional council was dissolved, and informally changed to Centre Européen pour la Recherche Nucléaire (European Centre for Nuclear Research).
CERN currently employs just under 3000 people full-time. Some 6500 scientists and engineers (representing 500 universities and 80 nationalities), about half of the world's particle physics community, work on experiments conducted at CERN.
The CERN accelerator complex has six main accelerators:
- Two linear accelerators generating low energy particles for injection into the Proton Synchroton. One is for protons and the other for heavy ions. These are known as Linac2 and Linac3 respectively.
- The PS Booster, which increases the energy of particles generated by the linear accelerators before they are transferred to the other accelerators.
- The 28 GeV Proton Synchroton (PS) built 1959.
- The Super Proton Synchrotron (SPS), a 2 km diameter circular accelerator built in a tunnel, which started operation in 1971. It originally had an energy of 300 GeV (but has been upgraded several times). As well as having its own beamlines for fixed-target experiments, it has been operated as a proton-antiproton collider, and for accelerating high energy electrons and positrons which were injected into the Large Electron Positron (LEP) collider.
- Isotope Separator On-line (ISOLDE), which was used to study unstable nuclei and first commisioned in 1967. Particles are initially accelerated in the PS Booster before entering ISOLDE.
It also has very impressive computer and wide-area networking facilities which are primarily used for experimental data analysis.
Most of the activities at CERN are currently directed towards building a new collider, the Large Hadron Collider (LHC) and the experiments for it, due to start operation in 2007. This will use the 9 km diameter circular tunnel previously occupied by LEP which was closed down in November 2000, and the PS/SPS complex to pre-accelerate protons which will be injected into it.
Decommissioned accelerators include:
- The original linear accelerator (Linac1).
- The 600 MeV Synchro-Cyclotron (SC) which started operation in 1957 and was shut down in 1991.
- The Intersecting Storage Rings (ISR), an early collider built in 1966
- LEP, which started operating in 1989.
- Low Energy Antiproton Ring (LEAR), comissioned in 1982. This assembled the first pieces of true antimatter, in 1995, consisting of nine atoms of antihydrogen. It was closed in 1996, and superseded by the Antiproton Decelerator.
There is also the Antiproton Decelerator (AD), which reduces the speed of antiprotons (which are created travelling at nearly the speed of light) for research into antimatter.
The World Wide Web began as a CERN project.
The original CERN signatories were:
- Federal Republic of Germany,
- The Netherlands,
- The United Kingdom,
- Austria joined in 1959
- Yugoslavia left in 1961, although in common with several other countries (and the European Union), it enjoys "observer status".
- Spain joined in 1961, left in 1969 and rejoined in 1983
- Portugal joined in 1985
- Finland and Poland joined in 1991
- Hungary joined in 1992
- Czechia and Slovakia joined in 1993
- Bulgaria joined in 1999
 According to Lew Kowarski, a former director of CERN, when the name was changed, and the acronym could have become the awkward OERN, Heisenberg said "But the acronym can still be CERN even if the name is ...