This fascicule on the medieval arts of poetry and prose emphasizes the Latin treatises. In order to demonstrate their significance - they are few in number - it has been necessary to locate them in the intellectual and scholastic milieux where they were used , and apart from which their real purpose would be, and has been, misunderstood. This will account for the rather large number of references to related or parallel genres. The treatises were part of a program of instruction that had links with and implication for a considerable variety of activities : reading, composition, interpretation, and instruction in grammar, rhetoric, and other arts and sciences, as well as in other kinds of composition like letterwriting, preaching, and scientific, historical, and moral instruction and writing. The vernacular treatises and manuals are discussed in Appendix II. Albeit more numerous than those written for Latin composition, for the most part they are more narrow in scope and elementary than their Latin counterparts. They are a small part of a large and very important phenomenon : the emergence and extension of the vernacular literatures in Western Europe.