EC-Earth started with the development of an atmosphere-ocean coupled general circulation model based on the seasonal forecasting system from the European Centre for Medium-Range Weather Forecasts (ECMWF). It consisted of a modified version of the atmosphere and land surface model from ECMWF's world-leading integrated forecasting system (IFS) coupled to the ocean and sea-ice model from the NEMO consortium. Meanwhile the model has evolved into an Earth system model, which includes modules for simulating dynamic vegetation, atmospheric chemistry, interactive aerosols, ocean biogeochemistry, the carbon cycle, and the Greenland ice sheet.