Codicology, like other disciplines, is a two-way process: out of the observation of single objects it builds a treasure-store of knowledge about the whole class of objects; and this knowledge is then applied in order to understand single objects. This last, the contribution to the comprehension of the individual codex, is probably the most important role of codicology. For the moment, we still have a long way to go towards a true comparative codicology that would include the Western and the Oriental traditions. In the following, I would like to illustrate the challenges of both sides of the discipline, drawing examples from Western codicology.