  The diffractive dissociation of a hadron at high energies, by either Coulomb
or Pomeron exchange, has a natural description in QCD as the materialization of
the projectile's light-cone wavefunctions; in particular, the diffractive
dissociation of a meson, baryon, or photon into high transverse momentum jets
measures the shape and other features of the projectile's distribution
amplitude. Diffractive dissociation can thus test fundamental properties of
QCD, including color transparency and intrinsic charm. All of these effects
have an impact on exclusive decays of $B$ mesons and the study of $CP$
violation. I also discuss recent work which shows that the structure functions
measured in deep inelastic lepton scattering are affected by final-state
rescattering, thus modifying their connection to light-cone probability
distributions. In particular, the shadowing of nuclear structure functions is
due to destructive interference effects from leading-twist diffraction of the
virtual photon, physics not included in the nuclear light-cone wavefunctions.
