This unique codex stands out among the historical bibliographic treasures in Catalonia and also represents an opportunity to debate on the failure of minimum intervention strategies when the latter are not preceded by an appropriate analysis of a book’s structural elements. The prayer book was originally kept in the Sant Jordi Chapel within the Palau de la Generalitat, the Government of Catalonia’s seat in Barcelona. Today, it is kept in the National Art Museum of Catalonia (MNAC).