New data on the pion – pion interaction at low energies

Current theoretical and experimental approaches to the pion – pion interaction are discussed and the results obtained are presented. Experiments on πN → ππN reactions as a source of information on ππ scattering are described as well as polarized target experiments and those on K_e4 decay and pionium. The concepts of effective field theory and the basic ideas of chiral perturbation theory are discussed. The problem of light scalar resonances is analyzed and the incorrectness of data analysis procedures is considered.