  We briefly discuss recent results on the evolution of unpolarized parton
densities and structure functions in massless perturbative QCD. Present partial
results on the next-to-next-to-leading order (NNLO) evolution kernels prove
sufficient for reliable calculations at not too small values of the Bjorken
variable, x > 10^-3. One order more can be taken into account at x >= 0.2.
Inclusion of these terms considerably reduces the main theoretical
uncertainties of determinations of alpha_s (to about 1% at the Z-mass) and the
parton densities from structure functions.
