DD4hep is a framework for the complete description of detector models based on a single source of information. When referring to the detector description this includes, in addition to the geometry and the materials used in the device, also parameters describing e.g. the detection techniques, constants required for alignment and calibration, description of the readout structures and conditions data. The main motivation behind the DD4hep framework is to devise a toolkit that addresses all these issues for all the stages of an experiment.