As part of digital humanities, the French National Library (BnF) strives to engage in public service of its heritage collections, its high-level technical resources and infrastructures, its skills, and know-how in the development of digital activities and its very active policy of collaboration with other institutions in France and abroad. These priorities are especially relevant in a research programme initiated by the French National Library and the British Library thanks to the patronage of The Polonsky Foundation. This twoand-a-half-year program (2016-2018) aims at cataloguing, digitizing and showcasing a corpus of 800 illuminated manuscripts, produced in France or England between the 8th and 12th centuries. The two libraries are working together to disseminate this corpus to the widest possible audience, digitizing 400 MSS from each library collection, cataloguing and partially restoring them. In addition, a general audience book richly illustrated will be published by the British Library, a symposium will be organized at the BnF, and two websites dedicated to the project will be developed. The BnF is currently creating a bilingual website based on the IIIF technology and the Gallica infrastructure (“Gallica marque blanche”) in order to collect all selected manuscripts and to allow digital comparison among them, while the British Library is preparing a bilingual website targeted for a general audience that will feature highlights from the most important of these manuscripts and articles commissioned by leading experts in the field. This paper aims to give an overview of the Polonsky programme, focusing on the main lines, the expectations and the targeted outputs of the programme; the digitization and restoration processes; the several scientific aspects that merge different disciplines and approaches in order to gain a better understanding of those fascinating cultural objects that are the manuscripts; finally, the challenges concerning the IIIF website and the interoperability of the metadata.