The operative concept of mediation has become central in research and reflections on communication, especially from the expansion and social influence of mass media, such as daily newspapers, radio and television, becoming mandatory entry of dictionaries relating to Science Communication. In the specialized field, along with compelling concepts such as mass media, culture industry and popular culture, it does not only widespread, as it has deserved special attention, such as Jesus Martin Barbero (a spanish, formed in Louvain, emigrated to Paris where he went to Colombia, where he established himself as a professor of communication) granted to it in articles, communications, interviews and books, notably in De los medios a las mediaciones (Barcelona, 1987). Your "culturalist" perspective won in South America a large reception and is easily used and quoted in articles and studies that claim to Library and Information Science. What this article argues is the refusal of the immediate and simplistic "import" of the concept. Instead, it argues a critical appropriation of the term, adjusting it to the specific subject of (re)constructed of Information Science, unitary and transdisciplinary that has been worked and taught at the University of Porto. The concept is discussed in the context of ongoing stress paradigm (the survival of the custodial and patrimonial paradigm and the emergence of new paradigm - post-custodial, informational and scientific), replicating itself, this tension: the custodial mediation which was formed and developed over the centuries. XIX-XX case and opposes mediation post-custodial with vague and uncertain on which urges stepping up research, the questions and hermeneutic exercises.