We report on recent results in perturbative Quantum Chromodynamics and its
generalization to Yang-Mills theories with fermions. We discuss the present
status of four-loop (N^3LO) calculations of the splitting functions for the
scale dependence (evolution) of the quark and gluon distributions of hadrons,
in particular the flavour non-singlet quark-quark case for which the complete
result has been obtained in the limit of a large number of colours. Five-loop
results are presented for the beta function, i.e., the running of the coupling
constant, for the hadronic decay of the Higgs boson in the heavy-top limit,
and for the lowest moment(s) of the non-singlet splitting functions.