The possible manifestations of New Physics beyond that predicted by the Standard Theory, which can be related to the existence of non-zero neutrino masses and neutrino mixing, are briefly discussed.
The phenomenology of 3-neutrino mixing, the present status of our knowledge about the 3-neutrino mixing parameters, including the absolute neutrino mass scale, and of the Dirac and Majorana CP violation in the lepton sector, are summarised. The current theoretical ideas about the origins i) of neutrino masses and of the enormous disparity between their values and the values of the charged lepton and quark masses, and ii) of the pattern of neutrino mixing revealed by the neutrino oscillation experiments, are reviewed, with the non-Abelian discrete symmetry approach considered in somewhat
greater detail. The possibilities to test these ideas are also briefly discussed.