When we speak of resource sharing, we mostly mean document sharing through union catalogues, list exchanges, interlibrary loans, cooperative acquisition programs... Yet, the first and primary condition of the library network efficiency is information sharing.

Libraries have been quite successful in this field for the last decades but, nowadays, new technology such as electronic mail or telefax offers unequaled facilities to set up and promote a permanent and world wide program of information exchanges liable to meet the increasing needs of punctual responses. From an eight year experience at Paris Observatory library which has been hosting the French national service CADIST [Centre d’acquisition et d’information scientifique et technique], we can assert that, outer demands of informations being at the same time useful information sources, such a quick answer service does participate to the improvement of the inner service efficiency.