Commissioning with cosmic rays of the muon spectrometer of the ATLAS experiment at the large hadron collider

The ATLAS experiment designed to exploit the full discovery potential of the Large Hadron Collider (LHC) at CERN, is currently being assembled and tested. Its Muon Spectrometer designed to measure muons in the final state from proton-proton interactions at the LHC with good momentum resolution (from 3% - 11% for muons of momentum of 1TeV), is being commissioned at the ATLAS cavern. It consists of four types of detectors, each using a different technology. Throughout this paper, a brief description of the commissioning procedure, the software tools developed and the first results obtained is given.