This paper deals with the development of computerized brain atlases addressing both research and clinical needs. The authors analyze in detail the potential of these systems and discuss the capabilities and limitations of the digital atlases currently being developed around the world. The authors propose to reconsider the concept of a brain atlas, regarding both its content, and the way it has to be used and managed in order to set up more effective cooperation between the user and the system. Particular emphasis is placed on extensibility and reuse issues. which are critical in this rapidly evolving field. These orientations result from both the authors' experience and the analysis of current trends in the field of neuroimaging. The general methodology is illustrated with examples related to computer aided surgical planning.