1983 - 1989
In 1976 a team in the ISR Division began studies of the design of the LEP machine. In 1978 the first practical design was published. In 1981 the final proposal was presented to the CERN Council. The proposal was to construct an electron-positron storage ring of 27 km circumference with four collision points (ALEPH, DELPHI, L3, OPAL) and an initial beam energy of about 50 GeV, sufficient for the production of the then hypothetical neutral boson Z°. In 1982 the ISR division was dissolved.

In 1983 most of the ISR staff moved to the new LEP division which was responsible for the construction of the new accelerator. In 1983 LEP construction work started. It was the largest civil-engineering work ever undertaken in Europe and was completed in 1988.

In 1990 LEP and SPS divisions merged to form SL (SPS+LEP) division. The operation of LEP was stopped in November 2000 and LEP was dismantled in the years 2001 and 2002 to clear the way for the LHC.