  Initial- and final-state interactions from gluon-exchange, normally neglected
in the parton model have a profound effect in QCD hard-scattering reactions,
leading to leading-twist single-spin asymmetries, diffractive deep inelastic
scattering, diffractive hard hadronic reactions, and nuclear shadowing and
antishadowing--leading-twist physics not incorporated in the light-front
wavefunctions of the target computed in isolation. I also discuss the use of
diffraction to materialize the Fock states of a hadronic projectile and test
QCD color transparency.
