  The Sun provides a standard reference against which we compare the chemical
abundances found anywhere else in the Universe. Nevertheless, there is not a
unique 'solar' composition, since the chemical abundances found in the solar
interior, the photosphere, the upper atmosphere, or the solar wind, are not
exactly the same. The composition of the solar photosphere, usually preferred
as a reference, changes with time due to diffusion, convection, and probably
accretion. In addition, we do not know the solar photospheric abundances,
inferred from the analysis of the solar spectrum using model atmospheres, with
high accuracy, and uncertainties for many elements exceed 25%. This paper gives
an overview of the methods and pitfalls of spectroscopic analysis, and
discusses the chemistry of the Sun in the context of the solar system.
