  We review the current status of perturbative corrections in QCD at four loops
for scattering processes with space- and time-like kinematics at colliders,
with specific focus on deep-inelastic scattering and electron-positron
annihilation. The calculations build on the parametric reduction of loop and
phase space integrals up to four-loop order using computer algebra programs
such as FORM, designed for large scale computations.
