Helped by his immense erudition, the author has reopened the file of Mongol diplomacy. In the present paper he surveys documents attesting of the Mongols’ faith in a mandate sent to them by the ‘Eternal Heaven (Möngke Tänggäri)’ for the conquest of the world. D. Morgan (“The Mongols and the Eastern Mediterranean,” in B. Arbel et al., eds., Latins and Greeks in the Eastern Mediterranean after 1204, London, 1989: 200) had questioned the self-perception by Genghis Khan as the master of the world. Through a linguistic analysis of the concept of tänggäri (‘heaven’) in the Secret History of the Mongols, Marie-Lise Beffa (“Le concept de tänggäri, ‘ciel’ dans l’Histoire secrète des Mongols,” Etudes mongoles et sibériennes 24 (1997): 215-36) has strongly discussed this thesis. However, as P. Jackson stresses at the beginning of his study (3-4), the Chinese sources clearly indicate that in his lifetime the Great Khan considered himself that he enjoyed a Heavenly Mandate. The Sung messengers were bearing tablets of authority (paiza) established by the Mongol chancery, on which the Heavenly Mandate is mentioned well before 1221. At the same time, it is for the most part in the letters sent by Genghis Khan’s successors toward the Latin West that the Heavenly Mandate given to the founder of the Mongol Empire and his successors is always invoked. The first letter attested is that addressed during the reign of Ögödei, in 1237, to the King of Hungary Bela iv. It was transmitted in Latin language by the Dominican monk Julian of Hungary (cf. Denis Sinor, “Un voyageur du treizième siècle: le Dominicain Julien de Hongrie,” Bulletin of the School of Oriental and African Studies 14/3 (1952): 589-602). The author then examines all the correspondences in which the Heavenly Mandate is mentioned, and he resituates them in the respective context of their elaboration. Besides P. Jackson’s subtle analyses, other interests of the present paper are its gathering of a large part of these texts with translations of large excerpts, and the rich bibliography on the Heavenly Mandate and on these correspondences. One can add that this ideology endured under the Ilkhans towards the Mamluk Sultanate, whence it strongly softened toward the Latin West.