  The Large Hadron-electron Collider LHeC is a proposed upgrade of the LHC. It
would add an electron beam to the LHC, and make it possible to study
electron-proton and electron-nucleus collisions at very high energies. We
present some of the highlights of the LHeC physics program related to the
studies of partonic structure of protons and nuclei, and to the non-linear QCD
phenomena visible at small $x$.
