The Proton Synchrotron (PS) is the oldest major particle accelerator at CERN, built as a 28 GeV proton accelerator in the late 1950s and put into operation in 1959. It takes the protons from the Proton Synchrotron Booster at a kinetic energy of 1.4 GeV and lead ions from the Low Energy Ion Ring (LEIR) at 72 MeV per nucleon. It has been operated as an injector for the Intersecting Storage Rings (ISR), the Super Proton Synchrotron (SPS) and the Large Electron-Positron Collider (LEP).