[en] In recent years, it has become more and more evident that repository development will involve a number of stages punctuated by interdependent decisions on whether and how to move to the next stage. These decisions require a clear and traceable presentation of technical arguments that will help in giving confidence in the feasibility and safety of the proposed concept. The depth of understanding and technical information available to support decisions will vary from step to step. A safety case is a key item to support the decision to move to the next stage in repository development. Progress is noted, in the past decade, in the performance and safety assessment areas, particularly in the methodologies for repository system analysis. Progress is also observed regarding the understanding of the natural system and its characterisation, treatment of uncertainties, and modelling. Some areas are under active development, e.g. the area of scenario development and analysis. Finally, to increase confidence, rigorous quality assurance procedures need to be implemented, as well as the factoring of the contribution of R and D in underground research laboratories. The paper summarises the lessons learnt within relevant NEA initiatives as they evolved over the course of a decade and now allow a comprehensive view of what constitutes a safety case. (author)