  Solar neutrino studies triggered and largely motivated the major developments
in neutrino physics in the last 50 years. Theory of neutrino propagation in
different media with matter and fields has been elaborated. It includes
oscillations in vacuum and matter, resonance flavor conversion and resonance
oscillations, spin and spin-flavor precession, etc. LMA MSW has been
established as the true solution of the solar neutrino problem. Parameters
theta12 and Delta_m21^2 have been measured; theta13 extracted from the solar
data is in agreement with results from reactor experiments. Solar neutrino
studies provide a sensitive way to test theory of neutrino oscillations and
conversion. Characterized by long baseline, huge fluxes and low energies they
are a powerful set-up to search for new physics beyond the standard 3nu
paradigm: new neutrino states, sterile neutrinos, non-standard neutrino
interactions, effects of violation of fundamental symmetries, new dynamics of
neutrino propagation, probes of space and time. These searches allow us to get
stringent, and in some cases unique bounds on new physics. We summarize the
results on physics of propagation, neutrino properties and physics beyond the
standard model obtained from studies of solar neutrinos.
