Commissioning and Performance of the ATLAS Transition Radiation Tracker with Cosmic Rays and First High Energy Collisions

The Transition Radiation Tracker is the outermost of the three subsystems in the ATLAS Inner Detector. It contributes significantly to the precision of the momentum measurement of charged particles and to the identification of electrons. This note reports about the recent commissioning progress and the performance achieved in preparation for first collisions at the LHC.