  For precision studies with QCD observables at colliders, higher order
perturbative corrections are often mandatory. For exclusive observables, like
jet cross sections or differential distributions, these corrections were until
recently only known to next-to-leading order (NLO) in perturbation theory.
Owing to many new technical developments, first next-to-next-to-leading order
(NNLO) QCD calculations are now becoming available. We review the recent
progress in this field.
