In 1996 CERN's antiproton machines – the Antiproton Accumulator (AC), the Antiproton Collector and the Low Energy Antiproton Ring (LEAR) – were closed down to free resources for the Large Hadron Collider. But a community of antimatter scientists wanted to continue their LEAR experiments with slow antiprotons. Council asked the Proton Synchrotron division to investigate a low-cost way to provide the necessary low-energy beams.

The resulting design report for the Antiproton Decelerator concluded:

The use of the Antiproton Collector as an antiproton decelerator holds the promise of delivering dense beams of 10⁷ protons per minutes and low energy (100 MeV/c) with bunch lengths down to 200 nanoseconds.

The Antiproton Declerator project was approved on 7 February 1997.