The CMS Electromagnetic Calorimeter (ECAL) is a high resolution, fine-grained calorimeter devised to measure photons and electrons at the LHC. Built of lead tungstate crystals, it plays a crucial role in the search for new physics as well as in precision measurements of the Standard Model. A pre-shower detector composed of sandwiches of lead and silicon strips improves pi0/gamma separation in the forward region. The operation and performance of the ECAL during the 2011 run at the LHC, with pp collisions at sqrt(s) = 7 TeV will be reviewed.
