  Rare kaon processes appear to be particularly suitable to study the
extensions of the standard model, especially if the possibility for eventual
direct evidence becomes unlikely. In this review, we discuss processes that are
important as a test of either the standard model or supergravity. Moreover,
some of these are important even for both the standard model and for
supergravity. Particular attention is paid to the reduction of uncertainties in
the calculation, especially the ones coming from the confinement effects.
Recent approaches, such as chiral perturbation theory, the large
$N_c$-expansion, QCD sum rules and lattice QCD, are discussed. This is found to
be the best strategy in view of the fact that supersymmetric effects are rather
tiny.
