Abstract and subjects
I discuss recent theoretical progress in rare (leptonic) decay modes of K and pi mesons. After briefly outlining the physics reach beyond the Standard Model (SM), I review the SM calculation of the ratios R(e/mu)(P) Gamma(P -> e (V) over bar (e)[gamma])/Gamma(P -> mu(V) over bar (mu)[gamma]) (P = pi, K) in Chiral Perturbation Theory to order e(2)p(4).