  I present a unified approach to calculating the next-to-next-to-leading order
(NNLO) soft and virtual QCD corrections to cross sections for electroweak,
Higgs, QCD, and SUSY processes. I derive master formulas that can be used for
any of these processes in hadron-hadron and lepton-hadron collisions. The
formulas are based on a unified threshold resummation formalism and can be
applied to both total and differential cross sections for processes with either
simple or complex color flows and for various factorization schemes and
kinematics. As a test of the formalism, I rederive known NNLO results for
Drell-Yan and Higgs production, deep inelastic scattering, and W+ gamma
production, and I obtain expressions for several two-loop anomalous dimensions
and other quantities needed in next-to-next-to-leading-logarithm (NNLL)
resummations. I also present new results for the production of supersymmetric
charged Higgs bosons; massive electroweak vector bosons; photons; heavy quarks
in lepton-hadron and hadron-hadron collisions and in flavor-changing neutral
current processes; jets; and squarks and gluinos. The NNLO soft and virtual
corrections are often dominant, especially near threshold. Thus, a unified
approach to these corrections is important in the search for new physics at
present and future colliders.
