Factorization for short distance hadron-hadron scattering

We show that factorization holds at leading twist in the Drell-Yan cross section dσ/dQ2dy and related inclusive hadron-hadron cross sections. We review the heuristic arguments for factorization, as well as the difficulties which must be overcome in a proof. We go on to give detailed arguments for the all order cancellation of soft gluons, and to show how this leads to factorization.