  Simple dynamics, few available decay channels, and highly controlled
radiative and loop corrections, make pion and muon decays a sensitive means of
exploring details of the underlying symmetries. We review the current status of
the rare decays: pi+ -> e+ nu, pi+ -> e+ nu gamma, pi+ -> pi0 e+ nu, and mu+ ->
e+ nu nu-bar gamma. For the latter we report new preliminary values for the
branching ratio B(E_gamma >10 MeV, theta_(e-gamma) > 30deg) = 4.365 (9)_stat
(42)_syst x 10^{-3}, and the decay parameter eta-bar = 0.006 (17)_stat
(18)_syst, both in excellent agreement with standard model predictions. We
review recent measurements, particularly by the PIBETA and PEN experiments, and
near-term prospects for improvement. These and other similar precise low energy
studies complement modern collider results materially.
