Report 89 revises and updates "The Commissioning and Routine Testing of Mammographic X-Ray Systems Report 59" first published in 1989, a standard reference in UK Medical Physics Departments. The emphasis of Report 89 is on the optimisation and assessment of the system as a whole. The report includes a new chapter on the theory and technology of digital imaging. Other revisions have been made to incorporate the testing of x-ray units with automatic beam optimisation software, changes to the new standard breast model, and to provide details on the methodology of image quality assessment.