  Broken chiral symmetry has become the basis for a unified treatment of
hadronic interactions at low energies. After reviewing mechanisms for
spontaneous chiral symmetry breaking, I outline the construction of the
low--energy effective field theory of the Standard Model called chiral
perturbation theory. The loop expansion and the renormalization procedure for
this nonrenormalizable quantum field theory are developed. Evidence for the
standard scenario with a large quark condensate is presented, in particular
from high--statistics lattice calculations of the meson mass spectrum. Elastic
pion--pion scattering is discussed as an example of a complete calculation to
O(p^6) in the low--energy expansion. The meson--baryon system is the subject of
the last lecture. After a short summary of heavy baryon chiral perturbation
theory, a recent analysis of pion--nucleon scattering to O(p^3) is reviewed.
Finally, I describe some very recent progress in the chiral approach to the
nucleon--nucleon interaction.
