  Dispersive approaches provide model independent description of meson-meson
scattering. We first review here the use of dispersion relations to obtain a
model independent unitarization of Chiral Perturbation Theory amplitudes, that
establish the existence of light scalar mesons and whose leading 1/N_c behavior
suggest they ahve a non q-qbar dominant component. We also review the forward
dispersion relation checks on conflicting experimental data and the resulting
very precise pion-pion scattering scattering amplitudes.
