We report on the operation and performance of the ATLAS Semi-Conductor Tracker(SCT), which has been functioning for 3 years in a high luminosity,high radiation environment. The SCT is constructed of 4088 silicondetector modules, for a total of 6.3 million strips. Each moduleoperates as a stand-alone unit, mechanically, electrically, opticallyand thermally. The modules are mounted into two types of structures:one barrel, made of 4 cylinders, and two end-cap systems made of 9disks. The SCT silicon micro-strip sensors are processed in the planarp-in-n technology. The signals are processed in the front-end ABCD3TAASICs, which use a binary readout architecture. Data is transferredto the off-detector readout electronics via optical fibres. We find99.3% of the SCT modules are operational, the noise occupancy andhit efficiency exceed the design specifications; the alignment is veryclose to the ideal to allow on-line track reconstruction and invariantmass determination. We will report on the operation and performance ofthe detector including an overview of the issues encountered. Weobserve a significant increase in leakage currents from bulk damagedue to non-ionizing radiation and make comparisons with thepredictions. We will also cover the time evolution of the keyparameters of the strip tracker, including the evolution of noise andgain, the measurement of the Lorentz angle and the tracking efficiencyin the harsh LHC environment. Valuable lessons for future siliconstrip detector projects will be presented.