Validation of the simulation of the CMS electromagnetic calorimeter using data

The CMS ECAL Collaboration developed a full simulation of the detector which is integrated in the software framework CMSSW. The simulation is based on the Geant4 tool for the description of particles interactions with the detector material. Care is given to the detailed description of the detector geometry and of the electronics response. The simulation software is fully operational and it is currently under validation using real data from testbeams and from commissioning with cosmic rays.