The previous decades have seen the effects of policies of "cultural democratisation" being combined with a growing involvement in the market for facilitating the access of the greatest number to the benefits of information and culture. Culture, entertainment and information have become the motors of the economy. Libraries have not quite got the measure of this moulding by the market of social demand. Their perception of demand continues to be infiltrated by a strategy of supply that is too uniform and by the behaviour that is expected of the user, of the reader. It is a matter of going beyond this attitude by encouraging new rapports with users and by working out in practical terms social demand by linking up rational and tactical analysis of needs and missions. Much more tomorrow rather than yesterday, librarians need to be conscious of the social dimension of their action and of their function as an interface between needs and products, which it will be necessary to select with more care in the midst of the plethora and the "flood". The responsibility of librarians with regard to the quality and relevance of resources made available is increasing.