  It is usually assumed -- following the parton model -- that the leading-twist
structure functions measured in deep inelastic lepton-proton scattering are
simply the probability distributions for finding quarks and gluons in the
target nucleon. In fact, gluon exchange between the outgoing quarks and the
target spectators effects the leading-twist structure functions in a profound
way, leading to diffractive leptoproduction processes, shadowing and
antishadowing of nuclear structure functions, and target spin asymmetries,
physics not incorporated in the light-front wavefunctions of the target
computed in isolation. In particular, final-state interactions from gluon
exchange lead to single-spin asymmetries in semi-inclusive deep inelastic
lepton-proton scattering which are not power-law suppressed in the Bjorken
limit. The shadowing and antishadowing of nuclear structure functions in the
Gribov-Glauber picture is due respectively to the destructive and constructive
interference of amplitudes arising from the multiple-scattering of quarks in
the nucleus. The effective quark-nucleon scattering amplitude includes Pomeron
and Odderon contributions from multi-gluon exchange as well as Reggeon
quark-exchange contributions. Part of the anomalous NuTeV result for
$\sin^2\theta_W$ could be due to the non-universality of nuclear antishadowing
for charged and neutral currents. Detailed measurements of the nuclear
dependence of individual quark structure functions are thus needed to establish
the distinctive phenomenology of shadowing and antishadowing and to make the
NuTeV results definitive. I also discuss diffraction dissociation as a tool for
resolving hadron substructure Fock state by Fock state and for producing
leading heavy quark systems.
