The Libellus de Diversis Ordinibus was written in the 1130s or 1140s, probably in the diocese of Liège, a recognized centre of religious and intellectual activity at the time. It is a description of the similarities and differences among the various orders of monks, canons, and hermits, and, though clearly a contribution to a contemporary debate, is more analytical than polemical. Its unknown author, 'R', perhaps a regular canon, builds his case by demonstrating how each order and profession corresponds to a group mentioned in the Old Testament: thus prefigured and performing their proper functions they all fill a legitimate place within the unity of the Church. It is an invaluable source for religious life in the twelfth century, offering detailed insights into contemporary assumptions and practice.