2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/125900Kl3 decays constitute, at present, the golden modes to extract |Vus| from experimental data. Its incertitude is dominated by the theoretical error in the determination of the vector form factor at zero transfer of momentum. I review the most relevant analytical approaches for the calculation of this parameter.5 pages, 1 figure. Talk given at the 4th International Workshop on the CKM Unitarity Triangle, CKM2006, 12th-16th December 2006, Nagoya (Japan). References corrected. Conclusions unchangedHigh Energy Physics - PhenomenologyHigh Energy Physics - ExperimentHigh Energy Physics - Latticetext