  Oscillations detected on the solar surface provide a unique possibility for
investigations of the interior properties of a star. Through major
observational efforts, including extensive observations from space, as well as
development of sophisticated tools for the analysis and interpretation of the
data, we have been able to infer the large-scale structure and rotation of the
solar interior with substantial accuracy, and we are beginning to get
information about the complex subsurface structure and dynamics of sunspot
regions, which dominate the magnetic activity in the solar atmosphere and
beyond. The results provide a detailed test of the modeling of stellar
structure and evolution, and hence of the physical properties of matter assumed
in the models. In this way the basis for using stellar modeling in other
branches of science is very substantially strengthened; an important example is
the use of observations of solar neutrinos to constrain the properties of the
neutrino.
