  This paper deals with Mellin transforms of rational functions $g/f$ in
several variables. We prove that the polar set of such a Mellin transform
consists of finitely many families of parallel hyperplanes, with all planes in
each such family being integral translates of a specific facial hyperplane of
the Newton polytope of the denominator $f$. The Mellin transform is naturally
related to the so called coamoeba $\mathcal{A}'_f:=\text{Arg}\,(Z_f)$, where
$Z_f$ is the zero locus of $f$ and $\text{Arg}$ denotes the mapping that takes
each coordinate to its argument. In fact, each connected component of the
complement of the coamoeba $\mathcal{A}'_f$ gives rise to a different Mellin
transform. The dependence of the Mellin transform on the coefficients of $f$,
and the relation to the theory of $A$-hypergeometric functions is also
discussed in the paper.
