After the fire at the Lyon universities' central library, consideration was made of the methods used to constitute new collections, in Language and Literature and the Humanities, for a research and study library constructed on the Gerland site and associated with the library of the École normale supérieure de Fontenay (Lettres). What does the concept ""core collection" signify? How does one progressively reconstitute holdings in response to the documentary needs of researchers and teachers stricken by the loss of essential resources? This essay has tried to bring forward some responses founded on the formalisation of an acquisition policy proposing to furnish documents and services, from detailed knowledge of the users and the axes of local university research. From a resolutely practical perspective, several tools to aid in selection are suggested.