This report is aimed at safety assessors of deep geological repositories and at technical specialists concerned with radioactive waste disposal. It is intended to improve communication among interested parties by clarifying the concepts related to the development of confidence, and by placing the various measures that are employed to evaluate, enhance and communicate confidence in the technical aspects of safety in a clear, logical framework. Thes measures are increasingly embodied in actual procedures applied in today’s safety assessments, and can be incorporated in a common framework, despite differences in approaches, practices and constraints both within and between repository projects.