Commissioning and Performance of the ATLAS Calorimeter System with Proton Collisions at the LHC

ATLAS is a general purpose detector located on the CERN Large Hadron Collider (LHC) which recorded its first proton-proton collisions at the end of 2009. Its calorimeter, very granular, hermetic in depth and covering 99% of the solid angle around the interaction point, is the central detector used to reconstruct electron, photon, jets, taus and missing transverse energy. The present hardware status is reviewed as well as the first in situ performance obtained with collision data.