iLOVECLIM is an intermediate complexity fully coupled climate Earth system model that aims at computation and understanding of the climate system on a millennial timescale. It is a code fork from the LOVECLIM climate model version 1.2. From its forerunner, iLOVECLIM retains only the physical climate components (atmosphere–ocean–terrestrial vegetation modules). It is developed further to progressively include the components necessary for multi-millennia palaeoclimate and future climate experiments. As such, iLOVECLIM is a tool designed to enhance the integration of model simulations and (palaeo-)data, with an emphasis on the simulation of isotopic tracers throughout all components of the climate system, as indicated by the i- prefix. The present, time-unlimited special issue hosts the technical documentation of the current version of iLOVECLIM as well as model evaluation manuscripts.