The ATLAS Collaboration operates a general purpose particle detector at the Large Hadron Collider at CERN. While the ATLAS detector design allows for a broad range of measurements and searches, it was strongly influenced by the desire to discover the Standard Model Higgs boson. An key component of the detector is its calorimetry, which aims at measuring the energy of particles and at identifying them. In this talk I will briefly present the ATLAS liquid argon calorimeter system, with emphasis on the considerations and constraints that led to its design and construction.