  We discuss the current state of what is known non-perturbatively about the
gluon propagator in QCD, with emphasis on the information coming from lattice
simulations. We review the specification of the lattice Landau gauge and the
procedure for calculating the gluon propagator on the lattice. We also discuss
some of the difficulties in non-perturbative calculations, especially Gribov
copy issues. We trace the evolution of lattice simulations over the past dozen
years, emphasizing how the improvement in computations has led not only to more
precise determinations of the propagator, but has allowed more detailed
information about it to be extracted.

High Energy Physics - Lattice