The perturbative QCD factorization approach in high energy nuclear collisons I will discuss the corrections to the perturbative QCD factorization approach in p+A and A+A reactions at RHIC and the LHC. These include a) nuclear size enhanced power corrections that lead to a suppression of single and double inclusive hadron production at forward rapidity at RHIC but disappear as a function of the transverse momentum; b) inelastic attenuation of the jet cross sections (jet quenching) that persists to much higher pT