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I summarize the history of theoretical predictions of, and experimentalattempts to measure, pion-pion (S-wave) scattering lengths. Recent measurementsat CERN confirm Weinberg's 1966 prediction of the I=2 scattering length andBasdevant and Lee's subsequent correction of the Weinberg I=0 value byinclusion of an S-wave I=0 resonance.

Pi-Pi Scattering Lengths in the Light of Precision Measurements