  The lectures review some of the basic concepts relevant for an understanding
of the low energy properties of the strong interactions: chiral symmetry,
spontaneous symmetry breakdown, Goldstone bosons, quark condensate. The
effective field theory used to analyze the low energy structure is briefly
sketched. As an illustration, I discuss the implications of the recent data on
the decay $K\to \pi\pi e\nu$ for the magnitude of the quark condensate.
