Modernization of the CMS Hadron Calorimetry at the LHC

The main areas for the development and modernization of the hadron calorimeter systems (HCAL) of the CMS experiment at the Large Hadron Collider (LHC) are reviewed. The results of the HCAL upgrade performed during the first and second long shutdowns of the LHC (LS1: 2013–2014 and LS2: 2019–2021) and immediate plans for the upgrades scheduled under the Phase 2 program for the third long shutdown of the LHC (LS3: 2025–2027) are discussed.