Idrisi's great geographical encyclopædia, Nuzhat al-muŠtāq al-āfāq, compiled in A.D. 1153 for King Roger II of Sicily, is formally arranged according to the seven Ptolemaic climates, each divided into ten “sections” numbered from west to east. In this arrangement, Ireland occupies the first section of the seventh climate, and Great Britain the second. Since Tuulio's publication of the third to fifth sections of this climate, it seems time that a comprehensive treatment should be attempted of the preceding two sections. Jaubert's pioneer French translation contains many attempts at identification of the place-names mentioned, which are not uniformly successful. Miller's Mappæ Arabicæ represents a considerable advance in this respect, but his identifications are not in every case acceptable, and even where correct they deserve some justificatory comment. In the following pages I have attempted to give all necessary comments, and to suggest some identifications which I believe to be an improvement on those hitherto proposed. I must express my grateful thanks to the Conservateur du Cabinet des Manuscrits of the Bibliothèque Nationale in Paris, and to the India Office Librarian in London, for the facilities which they have afforded me of consulting the manuscripts in those places; to Dr. W. B. Stevenson for generously allowing me to see the typescript of his article on Idrisi's map of Scotland before publication; to Professor I. Y. Krachkovskii and the Director of the Publichnaya Biblioteka for assisting me to obtain photographs of the Leningrad manuscript; and to Professor H. A. R. Gibb for some very helpful suggestions.