  We present a new resummation formula for the Drell-Yan cross section. The
formal resummation of threshold corrections in Drell-Yan hard-scattering
functions produces an exponent with singularities from the infrared pole of the
QCD running coupling. Our reformulation treats such `infrared renormalons' by a
principal value prescription, analogous to a modified Borel transform. The
resulting expression includes all large threshold corrections to the hard
scattering function as an asymptotic series in $\alpha_s$, but is a finite
function of $Q^2$. We find that the ambiguities of the resummed perturbation
theory imply the presence of higher twist corrections to quark-antiquark
hard-scattering functions that begin at $\Lambda_{QCD}/Q$. This suggests an
important role for higher twist in the phenomonolgy of hadron-hadron inclusive
cross sections. We also discuss the numerical evaluation of the exponent and
its asymptotic perturbation series for representative values of $Q^2$.
