PSalteRATIO develops its methodology from the convergence of genetic editing and traditional philological ecdotics. It analyses the rationale of a multilingual group of 12th-13th century metrical psalters (‘First French Metrical Psalter’, ‘Second French Metrical Psalter’, and the ‘Middle English Surtees Psalter’), similar to the Huguenot Psalter in terms of form but different in nature and function. Research will explore the connection of these three texts with French and English prose translations of the psalms dating back to the 12th-14th centuries. The study will also address the use of medieval exegetical literature (both Latin and in the vernacular, 11th-14th centuries) in the shaping of these metrical psalters. PSalteRATIO is based on an Open-Access corpus, whose end result is the publication of a joint digital edition of the aforementioned three texts and an all-encompassing study of their literary and genetic evolution. The project will be undertaken by four French partner teams with experience in the history of medieval French and English (language and literature) and digital humanities. They will be joined by two independently financed international teams from Czech Republic and Romania, in order to open a greater debate in philology, translatology, and ‘vernacular theologies’, which will lead to a common ERC Synergy project proposal in 2026. The theoretical and practical aspects of PSalteRATIO focus on translation automatisms and clusters (chief theoretical interest); links between vernacular and Medieval Latin tradition; comparatist literary approaches; sociolinguistics; cultural history; prosody; codicology and palaeography; textometry; and lexicography. These aspects will be discussed by the six partner teams in a series of seminars open to BA and MA students, with individual and collective papers published in the open-review journal of the project.