This is the proceedings of an international workshop on justification of medical exposure in diagnostic imaging, jointly organized by the IAEA and the European Commission. The workshop brought together experts from many countries and organizations to discuss how to ensure more effective application of justification in diagnostic imaging. Major areas that need action were identified, such as the coordination of methods and evidence used as a basis for clinical imaging recommendations, engagement of all relevant organizations in the deployment of these recommendations, and involvement of manufacturers and referring healthcare providers. Furthermore, the important role of education and training was re-emphasized. In the conclusion, the workshop participants highlighted that regulatory authorities have a key role in ensuring effective justification, and that an effective partnership with the medical community must be maintained to do this.