The purpose of the report was to report to the Parliament on how effectively and efficiently the Australian Taxation Office administers the Tax File Number System, and to identify opportunities for improvement of that system. The ANAO developed a methodological framework for the evaluation of the efficiency and effectiveness of the ATO's administration of the TFN system. The framework examined the TFN system; individuals and their TFNs; TFN withholding tax arrangements; and TFN information matching.