Large parton densities and high-pT physics in heavy-ion collisions

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.