If you have ever spilled coffee or left a stain on a book you were reading, then you will understand how accidental human interventions leave all sorts of traces in and on books. Medieval people were no different; they too accidentally left stains on their reading material. Historians of the book often see stains as inconveniences at best, and tragedies at worst. The Library of Stains project will examine a variety of stains found on parchment, paper, and bindings from medieval manuscripts, focusing only on “dirty” old books in order to gather scientific data that will provide clues as to how previous generations used and stored their reading material. The data will provide a new approach for learning about the history of the book, the materiality of books and book conservation.