  The ATLAS experiment is designed to study the proton-proton collisions
produced at the Large Hadron Collider (LHC) at CERN. Liquid argon sampling
calorimeters are used for all electromagnetic calorimetry as well as hadronic
calorimetry in the endcaps. After installation in 2004--2006, the calorimeters
were extensively commissioned over the three--year period prior to first
collisions in 2009, using cosmic rays and single LHC beams. Since then,
approximately 27 fb$\mathbf{^{-1}}$ of data have been collected at an
unprecedented center of mass energy. During all these stages, the calorimeter
and its electronics have been operating almost optimally, with a performance
very close to specifications. This paper covers all aspects of these first
years of operation.
  The excellent performance achieved is especially presented in the context of
the discovery of the elusive Higgs boson. The future plans to preserve this
performance until the end of the LHC program are also presented.
