  We explore the relation between resummation and explicit multi-loop
calculations for QCD hard-scattering amplitudes. We describe how the
factorization properties of amplitudes lead to the exponentiation of double and
single poles at each order of perturbation theory. For these amplitudes,
previously-observed relations between single and double poles in different 2 to
2 processes can now be interpreted in terms of universal functions associated
with external partons and process-dependent anomalous dimensions that describe
coherent soft radiation. Catani's proposal for multiple poles in
dimensionally-continued amplitudes emerges naturally.
