Gluon fusion is the main production mechanism for Higgs particles at t
he LHC. We present the QCD corrections to the fusion cross sections fo
r the Higgs boson in the Standard Model, and for the neutral Higgs bos
ons in the minimal supersymmetric extension of the Standard Model. The
QCD corrections are in general large and they increase the cross sect
ions significantly, In two steps preceding the calculation of the prod
uction processes, we determine the QCD radiative corrections to Higgs
decays into two photons and gluons.