Summary of $\pi$--$\pi$ Scattering Experiments

Present status of the study of the low energy $\pi \pi$ interaction is reviewed, including the recent results on reactions $\pi N\to \pi \pi N$ near threshold. Current experimental values of s-wave $\pi \pi$ scattering lengths are compared with predictions of various theoretical models. Required experimental and theoretical improvements are discussed, in particular the need for a new $K_{e4}$ decay measurement, and a more reliable theoretical interpretation of the near-threshold $\pi N\to \pi \pi N$ data.