  In the first part of these lectures the neutrino mixing hypothesis will be
considered in detail. We will discuss the possible schemes of neutrino mixing
and present the data of the recent experiments searching for effects due to
nonvanishing neutrino masses and mixing angles.In the second part of these
lectures the physics of solar neutrinos will be considered.We will discuss the
MSW resonance solution of the equation of evolution of a neutrino in matter and
present data of solar neutrino experiments.
