2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/39624I introduce and sketch the main features of those see-saw models where a large atmospheric mixing can be achieved starting from nearly diagonal matrices for charged leptons, Dirac neutrinos and Majorana right-handed neutrinos. It turns out that these models can be realized in Grand Unified Theories and they are well compatible with the related phenomenology of fermion masses and mixings.6 pages, LATEX, no figures. Contribution to the Proceedings of the XXXVth Rencontres de Moriond "ElectroWeak Interactions and Unified Theories", Les Arcs 1800, France, 11-18 March, 2000High Energy Physics - Phenomenologytext