  The completion of Run 1 of the CERN Large Hadron Collider has seen the
discovery of the Higgs boson and an unprecedented number of precise
measurements of the Standard Model, while Run 2 operation has just started to
provide first data at higher energy. Upgrades of the LHC to high luminosity
(HL-LHC) and the experiments (ATLAS, CMS, ALICE and LHCb) will exploit the full
potential of the collider to discover and explore new physics beyond the
Standard Model. In this article, the experimental challenges and the physics
opportunities in proton-proton collisions at the HL-LHC are reviewed.
