Realistic see-saw models of neutrino masses and mixing are briefly reviewed. It is shown that a rather small hierarchy of the mass scales governing neutrino oscillations can be obtained in models assuming a large hierarchy of the Dirac masses. The low energy mass spectrum of the active neutrinos is sensitive to unitary transformations for the right-handed neutrinos. Predictions for the mass spectrum of active neutrinos are discussed.

PACS numbers: 14.60.Pq, 12.15.Ff, 14.60.St