The earliest Old French herbal in verse, here edited for the first time, is a surprisingly comprehensive work (3188 octosyllables), based on an eleventh-century Latin treatise 'De viribus herbarum' attributed to a certain 'Macer'. It occupies a significant place in the development of herbals and is an interesting witness to writing in Western France in the thirteenth century and to the unusual syntax and concentrated style of its author. Some one hundred and twenty-five plants are described together with their medicinal uses, which cover a remarkable range of ailments. For ease of recognition the sections of text which do not seem to be based on the received text of 'Macer' are printed in italics. Quotations from the principal source and from parallels are given in the notes. This work will be of great value to all those interested in Old French, in medieval translation, the vernacular transmission of learning, and the history of medicine.