Die Dietsche boeke die ons toebehoeren is a codicological and paleographical study of 23 Middle Dutch manuscripts from the fourteenth century. All of them have survived from the Augustinian priory Rooklooster, just outside Brussels. It is believed that a great many vernacular books were produced in the local scriptorium of Rooklooster, both for use in the priory's library and for people outside this community, while the inhabitants also translated a number of Latin texts. Die Dietsche boeke die ons toebehoeren shows that the Middle Dutch manuscripts surviving from Rooklooster were, in fact, produced in the Charterhouse Herne, some thirty kilometers to the Southwest. The study describes the production of vernacular manuscripts in Herne and it shows the Charterhouse played an important role in the commercial book trade in the region Brussels: the Carthusians copied vernacular books at the request of citizens, religious communities and stationers.