  I discuss the role played by large parton densities in the QCD description of
high-pT observables in relativistic heavy-ion collisions. In pA collisions,
high-pT particles probe large parton densities in the nucleus and provide tests
of the Color Glass Condensate (CGC) picture of the small-x part of the nuclear
wave function. In AA collisions, high-pT particles carry information on both
the Quark-Gluon-Plasma phase, and the Glasma phase created at early times by
the collision of two CGCs.
