  These lecture notes concern recent developments in our understanding of the
low energy properties of QCD. Significant progress has been made on the lattice
and the beautiful experimental results on the Ke4 and K->3pi decays, as well as
those on pionic atoms also confirm the results obtained on the basis of Chiral
Perturbation Theory. There is an exception: one of the precision experiments on
Kmu3 decay is in flat contradiction with the Callan-Treiman relation. If
confirmed, this would indicate physics beyond the Standard Model: right-handed
quark couplings of the W-boson, for instance. Furthermore, I discuss two
examples where the estimates of the effective coupling constants based on
saturation by resonances appear to fail.
  In the second part, the progress made in extending the range of validity of
the effective theory with dispersive methods is reviewed. In particular, I draw
attention to an exact formula, which expresses the mass and width of a
resonance in terms of observable quantities. The formula removes the
ambiguities inherent in the analytic continuation from the real axis into the
complex plane, which plagued previous determinations of the pole positions
associated with broad resonances. In particular, it can now be demonstrated
that the lowest resonance of QCD carries the quantum numbers of the vacuum.
