  I discuss several theoretical tools which are useful for analyzing
perturbative and non-perturbative problems in quantum chromodynamics, including
(a) the light-cone Fock expansion, (b) the effective charge $\alpha_V$, (c)
conformal symmetry, and (d) commensurate scale relations. Light-cone Fock-state
wavefunctions encode the properties of a hadron in terms of its fundamental
quark and gluon degrees of freedom. Given the proton's light-cone
wavefunctions, one can compute not only the quark and gluon distributions
measured in deep inelastic lepton-proton scattering, but also the multi-parton
correlations which control the distribution of particles in the proton
fragmentation region and dynamical higher twist effects. Light-cone
wavefunctions also provide a systematic framework for evaluating exclusive
hadronic matrix elements, including timelike heavy hadron decay amplitudes and
form factors. The $\alpha_V$ coupling, defined from the QCD heavy quark
potential, provides a physical expansion parameter for perturbative QCD with an
analytic dependence on the fermion masses which is now known to two-loop order.
Conformal symmetry provides a template for QCD predictions, including relations
between observables which are present even in a theory which is not scale
invariant. Commensurate scale relations are perturbative QCD predictions based
on conformal symmetry relating observable to observable at fixed relative
scale. Such relations have no renormalization scale or scheme ambiguity.
