An encyclopaedic collection in itself, public library has always been a place for the consultation of encyclopaedias. Wikipedia is an open encyclopaedia, free and written cooperatively. At first glance, such a project appears truly utopist, even criticisable. Nevertheless, both international and multilingual, it works well and is enjoying rapid growth. It uses Wiki technology and is published under a free documentary licence. Within several years, even months, Wikipedia could have an important place in libraries. French speaking librarians could improve it by contributing to it.