  The rare decays of the $K$ meson have had a long tradition as a laboratory
for testing the symmetry properties of the weak interactions, and the manner in
which these symmetries are broken by higher order effects. Present--day
interest is focussed on decays that are suppressed by $CP$--symmetry or GIM
symmetry. Such decays, in the standard theory, are sensitive to effects of the
virtual top quark, and could also reveal new interactions transcending the
standard model. In addition, the radiative decays of the $K$ meson have become
a useful testing--ground for effective Lagrangians describing the low energy
interactions of pions, kaons and photons.
