Commissioning of the ATLAS detector and combined beam test results

The ATLAS detector is a large and complex experiment. Commissioning of the various components, both separately and together, is a challenging task which requires a methodology and a sustained and detailed plan of work. The commissioning stages of ATLAS will be described, together with an overview of results obtained during the construction and the integration so far. Once installed and functional, the various parts of the detector are operated with cosmic particles in several combinations. The performance of the detector components, both individually and in combination, has been also measured in a series of test beam data taken over the last years.