Fibre Optic Reflectance Spectroscopy (FORS) is a non-invasive method which has been widely used during the past 15 years for the study of pre-modern books and manuscripts.Using a fibre-optic probe and a broad band light source, FORS measures the spectrum of light reflected off inks, pigments, and parchment, spanning the ultraviolet, visible, and near-infrared range.Because different materials absorb and reflect light uniquely, FORS enables researchers to identify specific substances, such as plant dyes, mineral pigments, or iron-gall ink, in situ and without requiring any sampling. By combining FORS data with other scientific and historical analyses, it is possible to reconstruct not only the visual and material composition of medieval manuscripts but also part of their production history and subsequent interventions, making FORS an indispensable tool for this project.