  Rare decays of K mesons are reviewed from the perspective of testing the
``ones'' and ``zeros'' of the standard model. Decays K^+ -> pi^+ nu anti-nu and
K_L -> pi^0 nu anti-nu probe the one-loop effective Hamiltonian for s -> d nu
anti-nu, and can constrain the rho, eta coordinates of the unitarity triangle.
Decays such as K_L -> pi^0 l^+ l^-, K_L -> mu^+ mu^-, K^+ -> pi^+ l^+ l^- and
K_L -> pi^+ pi^- e^+ e^- involve short-distance effects, as well as
long-distance photon-induced contributions. Some comments are added on curious
features of electroweak amplitudes in the ``gaugeless'' limit, and in the
chiral electron limit m_e -> 0.
