The CMS electromagnetic calorimeter at the LHC

The CMS experiment at the CERN Large Hadron Collider has placed great emphasis on precise calorimetry for electrons and photons. The electromagnetic calorimeter (ECAL) contains about 75 000 scintillating lead tungstate crystals that are read out using sophisticated electronics. This paper will describe the ECAL and the experimental factors that influenced the choice of the technologies used in the detector design. The barrel ECAL has been installed into the experiment and installation of the endcaps will commence in early 2008. The pre-calibration and commissioning of these detectors will be described and the current status of the ECAL reviewed. The prospects for the initial operation period in 2008, when beams are first collided in the LHC, will be discussed.