  I discuss the systematic modifications to the perturbative QCD factorization
approach in high energy l+A, p+A and A+A reactions. These include transverse
momentum diffusion manifest in the Cronin effect and a small increase in the
dijet acoplanarity; nuclear size enhanced power corrections that lead to
shadowing in deeply inelastic scattering and suppression of single and double
inclusive hadron production at forward rapidity at RHIC but disappear as a
function of the transverse momentum; inelastic attenuation of the jet cross
sections or jet quenching that persists to much higher pT.
