  We review techniques simplifying the analytic calculation of one-loop QCD
amplitudes with many external legs, for use in next-to-leading-order
corrections to multi-jet processes. Particularly useful are the constraints
imposed by perturbative unitarity, collinear singularities and a
supersymmetry-inspired organization of helicity amplitudes. Certain sequences
of one-loop helicity amplitudes with an arbitrary number of external gluons
have been obtained using these constraints.
