  In this lecture we review some of the basic properties of neutrinos, in
particular their mass and the oscillation behavior. First we discuss how to
describe the neutrino mass. Then, under the assumption that neutrinos are
massive and mixed, the fundamentals of the neutrino oscillations are discussed
with emphasis on subtle aspects which have been overlooked in the past. We then
review the terrestrial neutrino oscillation experiments in the framework of
three generations of neutrinos with the standard mass hierarchy. Finally, a
brief summary of the current status of the solar and atmospheric neutrino
problems will be given.
