When compiling the short-title catalogue of books printed in the sixteenth-century northern Netherlands from 1541 to 1600, Paul Valkema Blouw was confronted with a large number of ‘problem cases’, such as anonymously and/or surreptitiously printed editions, fictitious printers and undated or falsely dated printed works. By minutely analysing the typefaces, initials, vignettes and other ornaments used, drawing from his extensive knowledge of secondary literature, archival information and his unrivalled typographic memory, he not only managed to attribute a surprising number of these publications to a printer, but also could establish the period of time in which, as well as the places where, they must have been printed. These findings and the ways in which they were reached are described in the present collection of papers. They are of paramount importance to scholars engaged in research of the period concerned, whether in the field of church history, national history or book history