  When calculating next-to-leading order QCD cross sections, divergences in
intermediate steps of the calculation must be regularized. The final result is
independent of the regularization scheme used, provided that it is unitary. In
this paper we explore the relationship between regularization scheme
independence and unitarity. We show how the regularization scheme dependence
can be isolated in simple universal components, and how unitarity can be
guaranteed for any regularization prescription that can consistently be
introduced in one-loop amplitudes. Finally, we show how to derive transition
rules between different schemes without having to do any loop calculations.
