The Large Electron–Positron Collider (LEP) was one of the largest particle accelerators ever constructed.
It was built at CERN, a multi-national centre for research in nuclear and particle physics near Geneva, Switzerland. LEP was a circular collider with a circumference of 27 kilometres built in a tunnel straddling the border of Switzerland and France. It was used from 1989 until 2000. To date, LEP is the most powerful accelerator of leptons ever built.