  The performance of the electromagnetic calorimeter of the ALICE experiment
during operation in 2010-2018 at the Large Hadron Collider is presented. After
a short introduction into the design, readout, and trigger capabilities of the
detector, the procedures for data taking, reconstruction, and validation are
explained. The methods used for the calibration and various derived corrections
are presented in detail. Subsequently, the capabilities of the calorimeter to
reconstruct and measure photons, light mesons, electrons and jets are
discussed. The performance of the calorimeter is illustrated mainly with data
obtained with test beams at the Proton Synchrotron and Super Proton Synchrotron
or in proton-proton collisions at $\sqrt{s}=13$ TeV, and compared to
simulations.
