  Light-front coordinates offer a scenario in which a constituent approximation
of hadron structure can emerge from QCD. This requires cutoffs that violate
Lorentz covariance and gauge invariance, and a new renormalization group
formalism based on a similarity transformation is used with coupling coherence
to fix counterterms that restore these symmetries. The counterterms contain
functions of longitudinal momentum fractions which severely complicate
renormalization, but they also offer possible resolutions of apparent
contradictions between the constituent picture and QCD. The similarity
transformation and coupling coherence are applied to QED; and it is shown that
the resultant Hamiltonian leads to the correct bound state results. The same
techniques are applied to QCD and it is shown that a simple confinement
mechanism and a reasonable description of heavy quark bound states emerge
naturally.
