Five-Loop Running of the QCD Coupling Constant

We analytically compute the five-loop term in the beta function which governs the running of as-the quark-gluon coupling constant in QCD. The new term leads to a reduction of the theory uncertainty in as taken at the Z-boson scale as extracted from the t-lepton decays as well as to new, improved by one more order of perturbation theory, predictions for the effective coupling constants of the standard model Higgs boson to gluons and for its total decay rate to the quark-antiquark pairs.