  The original B. Pontecorvo idea of neutrino oscillations is discussed.
Neutrino mixing and basics of neutrino oscillations in vacuum and in matter are
considered. Recent evidences in favour of neutrino oscillations, obtained in
Super-Kamiokande, SNO, KamLAND and other neutrino experiments are discussed.
Neutrino oscillations in the solar and atmospheric ranges of the neutrino
mass-squared differences are considered in the framework of the minimal scheme
with the mixing of three massive neutrinos. Results of the tritium beta-decay
experiments and experiments on the search for neutrinoless double-beta-decay
are briefly discussed.
