  Assuming neutrino oscillations occur, the pp electron neutrino flux is
uncertain by at least a factor of two, the ${\rm ^8B}$ flux by a factor of
five, and the ${\rm ^7Be}$ flux by a factor of forty-five. Calculations of the
expected results of future solar neutrino experiments (SuperKamiokande, SNO,
BOREXINO, ICARUS, HELLAZ, and HERON) are used to illustrate the extent to which
these experiments will restrict the range of the allowed neutrino mixing
parameters. We present an improved formulation of the ``luminosity constraint''
and show that at 95\% confidence limit this constraint establishes the best
available limits on the rate of creation of pp neutrinos in the solar interior
and provides the best upper limit to the ${\rm ^7Be}$ neutrino flux.
