Calorimetry: Introduction, Overview and physics requirement at HL-LHC

We discuss how the HL-LHC luminosity target and Phase II physics goals drive the Calorimeter performance requirements of the LHC experiments, and motivate the program of Upgrades being developed to address these. Radiation damage to detector and electronics components will impose challenges to the operation of the existing calorimeter systems and will limit their lifetime. Instantaneous luminosities above the nominal LHC values may induce significant degradation in the response of some detectors (in particular in the forward region). To optimize the performance of the systems and cope with the physics goals in Phase-II the trigger system will set new requirements for the calorimeter readout.