  Light-front coordinates offer a scenario in which a constituent picture of
hadron structure can emerge from QCD, after several difficulties are addressed.
Field theoretic difficulties force us to introduce 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
cuonterterms that restore these symmetries. The counterterms contain functions
of longitudinal momentum fractions that 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 standard lowest order bound state results, with the Coulomb
interaction emerging naturally. The same techniques are applied to QCD and with
physically motivated assumptions it is shown that a simple confinement
mechanism appears.
