  The predictions of an improved standard solar model are compared with the
observations of the four solar neutrino experiments. The improved model
includes premain sequence evolution, element diffusion, partial ionization
effects, and all the possible nuclear reactions between the main elements. It
uses updated values for the initial solar element abundances, the solar age,
the solar luminosity, the nuclear reaction rates and the radiative opacities.
Neither nuclear equilibrium, nor complete ionization are assumed. The
calculated $^8$B solar neutrino flux is consistent, within the theoretical and
experimental uncertainties, with the solar neutrino flux measured by
Kamiokande. The results from the $^{37}$Cl and $^{71}$Ga radiochemical
experiments seem to suggest that the terrestrial $^7$Be solar neutrino flux is
much smaller than that predicted. However, the present terrestrial ``defecit''
of $^7$Be solar neutrinos may be due to the use of inaccurate theoretical
neutrino absorption cross sections near threshold for extracting solar neutrino
fluxes from production rates. Conclusive evidence for a real deficit of $^7$Be
solar neutrinos will require experiments such as BOREXINO or HELLAZ. A real
defecit of $^7$Be solar neutrinos can be due to either astrophysical reasons or
neutrino properties beyond the standard electroweak model. Only future neutrino
experiments, such as SNO, Superkamiokande, BOREXINO and HELLAZ, will be able to
provide conclusive evidence that the solar neutrino problem is a consequence of
neutrino properties beyond the standard electroweak model. Earlier indications
may be provided by long baseline neutrino oscillation experiments.
