  Helioseismology has allowed us to study the structure of the Sun in
unprecedented detail. One of the triumphs of the theory of stellar evolution
was that helioseismic studies had shown that the structure of solar models is
very similar to that of the Sun. However, this agreement has been spoiled by
recent revisions of the solar heavy-element abundances. Heavy element
abundances determine the opacity of the stellar material and hence, are an
important input to stellar model calculations. The models with the new, low
abundances do not satisfy helioseismic constraints. We review here how
heavy-element abundances affect solar models, how these models are tested with
helioseismology, and the impact of the new abundances on standard solar models.
We also discuss the attempts made to improve the agreement of the low-abundance
models with the Sun and discuss how helioseismology is being used to determine
the solar heavy-element abundance. A review of current literature shows that
attempts to improve agreement between solar models with low heavy-element
abundances and seismic inference have been unsuccessful so far. The
low-metallicity models that have the least disagreement with seismic data
require changing all input physics to stellar models beyond their acceptable
ranges. Seismic determinations of the solar heavy-element abundance yield
results that are consistent with the older, higher values of the solar
abundance, and hence, no major changes to the inputs to solar models are
required to make higher-metallicity solar models consistent with helioseismic
data.
