Changing any system is difficult, but that has not discouraged public libraries. 108 establishments have already changed software packages and 200 large libraries are going to « re-computerize » before the year 2000. The disappearance of products, buying back by suppliers, the search for a computing standard, the gaps in old systems and the global spread of supply are the engines of this massive re-equipment. More specifically, « re-computerization » is today inscribed in an approach known as « information systems » and has lead to the implementation of several new software packages, to the reprocessing of data... and all this without any interruption in service ! After the drawing up of a complex schedule, public libraries must learn to choose between tenders that may sometimes mislead and may not offer an ideal system. Finally, they must organize their exploitation of software packages to take better advantage of them. The importance of the stakes and the difficulties underline a key factor for success : the application from the start of an inclusive approach.