The paper outlines the main steps of Catholic Church’s politics against the vernacular languages and shows the effect it had on some specific areas of book production. The relationship between the Catholic Church and the vernacular languages was neither unequivocal nor linear during the early modernity. From an initially favorable attitude towards their use, during the sixteenth century the Catholic Church became more and more suspicious and mistrustful. In order to characterize the changing fortunes of the vernacular, this paper does not only consider the three indices of prohibited books promulgated in 1558, 1564 and 1596, usually examined by scholars, but focuses also on a series of instruments never officially institutionalized intended to have an incisive impact on the book production.