An electromagnetic calorimeter is used to measure the energy of the scattered leptons, and to discriminate between leptons, photons and hadrons. The instrument is made out of Pb-glass, and was built by NIKHEF in collaboration with groups from Frascati and Yerevan. The Pb-glass can be moved out of the vicinity of the beam during injection, ramping and tuning of the lepton beam. The entire system is operating without any problem since the beginning of data taking at HERMES. Operationally, a separation of responsibilities was made: Frascati is in charge of the day-to-day operation and calibration of the calorimeter, while NIKHEF has taken responsibily for the operation and maintenance of the driving mechanism.