Commissioning and Operation of the CMS Electromagnetic Calorimeter

The operation and general performance of the CMS electromagnetic calorimeter using cosmic-ray muons recorded after the closure of CMS in late 2008 are described. The overall status of the 75,848 channels corresponding to the crystal barrel and endcap detectors is reported. The stability of crucial operational parameters, such as high voltage, temperature and electronic noise, is summarised and the performance of the light monitoring system is presented. The status of the barrel, endcap and preshower detectors following additional cosmic-ray muon tests in 2009 is also summarised.