  The present status of the solar neutrino problem is reviewed. The strongest
motivation for new neutrino physics comes from the complete phenomenological
failure of astrophysical solutions: (1) The standard solar model is excluded by
each of the solar neutrino experiments. (2) The combined results of Homestake
and Kamiokande are incompatible with any astrophysical solution. (3) Even if
the Homestake results were ignored entirely, there is no realistic solar model
so far that describes the Kamiokande and gallium data simultaneously within
their experimental uncertainties. On the other hand, the MSW solutions provide
a complete description of the data, strongly hinting at the existence of mass
and mixing of neutrinos. The MSW predictions for the future experiments are
given in detail. It is stressed that solar model uncertainties are significant
in determining the oscillation parameters and in making predictions for the
future experiments. Especially, a $^8$B flux (or $S_{17}$) smaller by 20\% than
that of the Bahcall-Pinsonneault model can make the interpretation of the
charged to neutral current ratio measurement in SNO ambiguous.
