My project investigates how a courtly space of knowledge, namely court libraries, shaped the textual practices related to the manuscripts and books preserved there. The organization of a library influenced not only the epistemological delimitation of a certain subject, but also determined whether certain texts were present, catalogued, and how far they were accessible for use. Since a textual practice is hardly conceivable in isolation from the “space” where it was carried out, this chapter argues that a court library was constitutive of the textual practices carried on within its walls. As a laboratory for this argument and a guide through the understanding of late Renaissance court libraries, I consider the subject catalogue “De Turcis et contra Turcas” drawn up by the imperial librarian in Vienna Hugo Blotius in 1576. This catalogue embodies the three main ingredients shaping the “agenda” of a court library in the late Renaissance: the political projects, scholarly projects, and the space of the library. It treated a subject of political importance that would arouse the curiosity of the emperor and his Viennese entourage, and it was intellectually and technically part of a universal library project, and had a circulation and an impact on the scholarly community that went well beyond the library's walls. In my project I therefore use the catalogue de Turcis et contra Turcas to highlight the interactions between knowledge systematization and scholarly practices in the libraries, drawing out the implications of this interaction when library catalogues began to be used and to circulate following unexpected trajectories.