  We discuss radiative corrections to K_{e3} and pi_{e3} decays within chiral
perturbation theory with virtual photons and leptons. We then present the
extraction of the CKM elements V_{us} and V_{ud} using the presently available
experimental input. Finally, we discus the test of CKM unitarity based on the
present independent knowledge of V_{ud} and V_{us}, and describe the prospects
of improvement with the upcoming B.R. measurements.
