  Hadron-hadron scattering lengths are fine probes of our understanding of
nonperturbative QCD. I discuss the status of a variety of scattering processes
sensitive to the spontaneous and explicit chiral symmetry breaking of QCD, such
as pion-pion, pion-kaon, pion-nucleon, antikaon-nucleon and Goldstone boson
scattering off D-mesons. The fruitful interplay of theory, experiment and
lattice QCD is emphasized. I point out what has to be done in these fields to
gain further insight into these fundamental parameters.
