The article analyzes the major changes of the display systems of bibliographic data occurred over the past 20 years. The catalogue is examined as a communication tool in relation with the new technologies that allow its understanding and use. The online catalogs accessible offsite, outside the library, have changed with the evolution of technology and of the Web. They stay beside and together with other kind of contents attainable through the library, while libraries are testing the centralization of access. New actors and cataloguing tradition are experiencing new communication systems, the librarianship is choosing if stay outside or inside this process.