The physics of gluon saturation and non-linear evolution at small values of
parton momentum fraction x in the proton and nucleus is discussed in the
context of experimental results at HERA and RHIC. The rich physics potential of
low-x QCD studies at the LHC is discussed and some measurements in pp, pA and
AA collisions accessible with the Compact Muon Solenoid (CMS) experiment are
presented.Comment: Extended clarifications to Eq. (6). A couple of typos corrected. To
appear in EPJ
