Mary of Guelders’ richly illuminated prayer book, written by Helmich die Lewe and completed in 1415, is extraordinary for several reasons: it originally consisted of more than 600 folia, it is richly illuminated, it was written in the Lower Rhine vernacular, and it contains an unusual compilation of prayers, hours and components of a breviary. These past few years the book has been the focus of a research project spearheaded by the Staatsbibliothek zu Berlin and Radboud University in Nijmegen. Their hard work has yielded enough noteworthy results to deserve its own exhibition which will open in Museum Het Valkhof on 13 October 2018 and will run until 6 January 2019. It will feature the research’s findings on the comprehensive and complex prayer book, the life of Mary, Duchess of Jülich and Guelders, and cultural developments in the duchies of Guelders, Jülich and Berg. To mark the occasion of the exhibition entitled ‘I, Mary of Guelders. The duchess and her extraordinary prayer book’ Radboud University is organising a two-day conference in Nijmegen together with Museum Het Valkhof and the Staatsbibliothek zu Berlin.