Since the creation of the first Central Lending Libraries in 1945, the missions of these services decentralized in 1986 and then titled Regional Lending Libraries have changed deeply. At first, these County Libraries have been in charge of the diffusion of books in rural areas by library-bus, this logic of distribution has been adapted to peculiar conditions of each County. Then, to be coherent and complementary, the notion of network has grown up : the County Library becoming an unifying departmental institution. The County Libraries are involved in projects of national and regional development in which their role has to be acknowledged. To guarantee access to knowledge and to information sources for all, to be included in the national document menu, they will have to invent new kinds of cooperation with other institutions.