Unique case in Europe, inheritance of the French Revolution, some five million ancient books (excepting the National library collections, and the XIXth century editions) are owned by some four or five hundred public libraries. These collections contents are partly unknown. The most imperative task is to locate and to inventory them. This urgent work has to preceed preservation and restoration measures, which depend on what will be found on the shelves. Different projects, for the creation of regional conservation centers, represent a good opportunity to begin such an essential work, by photographying title-pages, using computers and the STC cataloguing methods... These pages would persuade librarians and local politicians of the importance of this task, before deciding expensive conservation and restoration campaigns.