This report describes the physical core of the new CMCC Earth System Model CMCC–CESM–NEMO. The model is largely based on the Community Earth System Model (CESM) project developed at the National Center for Atmospheric Research (NCAR). The ocean component of the CESM model has been replaced by the Nucleus for European Modelling of the Ocean (NEMO) general circulation model, developed by an European consortium of modelling centers of which the CMCC is an active member. An overview of the CMCC–CESM–NEMO model is provided, together with a detailed description of the integration of NEMO into CESM and of the design of the physical coupling interface.