CMS Electromagnetic Trigger commissioning and first operation experiences

The CMS electromagnetic calorimeter (ECAL) is a high-resolution calorimeter made of 75848 lead tungstate crystals and optimized for the discovery of the Higgs boson in its two photon decay mode. In view of the high raw event rate at the Large Hadron Collider, the ECAL Trigger will play a major role. This paper reviews the strategy and the tests completed to ensure that the ECAL Trigger reaches the required specifications. The results from the commissioning and the first experiences with cosmic ray data are presented.