  We investigate the perturbative and nonperturbative renormalization of
composite operators in lattice QCD restricting ourselves to operators that are
bilinear in the quark fields (quark-antiquark operators). These include
operators which are relevant to the calculation of moments of hadronic
structure functions. The nonperturbative computations are based on Monte Carlo
simulations with two flavors of clover fermions and utilize the
Rome-Southampton method also known as the RI-MOM scheme. We compare the results
of this approach with various estimates from lattice perturbation theory, in
particular with recent two-loop calculations.
