The IAEA has a long-standing history of providing radiotherapy dosimetry audits in its Member States. This publication summarizes the methodologies resulting from the work of four coordinated research projects (CRPs) and offers information on experiences collected during the development of dosimetry audit programmes and their implementation at national levels. It also sets the framework and provides advice on the structure of dosimetry audit centres and discusses the general approach for audit development and the necessary background to conduct dosimetry audits in radiotherapy by national organizations. It provides technical and scientific details, as well as practical experiences of the audit steps developed under these CRPs. Any organization developing national audit programmes for radiotherapy can use this publication as a reference and to learn from the experiences of other national audit networks.