  Certainly one of the most exciting areas of research at present is neutrino
physics. The neutrinos are fantastically numerous in the universe and as such
they have bearing on our understanding of the universe. Therefore, we must
understand the neutrinos, particularly their mass. There is compelling evidence
from solar and atmospheric neutrinos and those from reactors for neutrino
oscillations implying that neutrinos mix and have nonzero mass but without
pinning down their absolute mass. This is reviewed. The implications of
neutrino oscillations and mass squared splitting between neutrinos of different
flavor on pattern of neutrino mass matrix is discussed. In particular, a
neutrino mass matrix, which shows approximate flavor symmetry where the
neutrino mass differences arise from flavor violation in off-diagonal Yukawa
couplings is elaborated on. The implications in double beta decay are also
discussed.
