  The recent progress in establishing the existence of finite neutrino masses
and mixing between generations of neutrinos has been remarkable, if not
astounding. The combined results from studies of atmospheric neutrinos, solar
neutrinos, and reactor antineutrinos paint an intriguing picture for theorists
and provide clear motivation for future experimental studies. In this review,
we summarize the status of experimental and theoretical work in this field and
explore the future opportunities that emerge in light of recent discoveries.
