The Large Electron-Positron Collider (LEP) is a particle accelerator that was operated at CERN on the outskirts of Geneva, Switzerland, from 1989 to 2000. LEP accelerated counterpropagating beams of electrons and positrons in a 27 km diameter synchrotron ring. With a total collision energy of 209 GeV, LEP was the most powerful electron-positron collider ever built. Notably, LEP enabled a precision measurement of the mass of W and Z bosons, which provided solid experimental support for the Standard Model. In 2000, LEP was dismantled to make space for the LHC, which was built in its place.