2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/42491We 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.References added, Eq. 25 corrected. 8 pages, 1 figure, 2 tables, Talk given at the 38th Rencontres de Moriond on Electroweak Interactions and Unified Theories, Les Arcs, France, March 15-22 2003High Energy Physics - Phenomenologytext