As the author puts it, biographic dictionaries are not often used for the history of the Mongol Empire, and such has long been the case of the Majma‘ al-adab fi mu‘jam al-alqab by Ibn al-Fuwati. The work compiles bibliographic data on writers, scholars and statesmen from the world of Islam within the western territories of the Mongol Empire (the Il-Khanate). It is true that the work has survived incomplete, and that the life of the author is not easy to reconstruct, since only fragments of it are known to us. Ibn al-Fuwati died in January 1323 and wrote the major part of its dictionary between 1312-16 from books, literary (or not) materials and interviews with contemporaries. We currently have at our disposal 5,291 entries of his work. In spite of the composite image that Ibn al-Fuwati gives of transfers and cultural exchanges under Mongols in literature, astronomy or case law, his work does has yet not benefitted from a comprehensive study. In the present article D. DeWeese uses some examples for casting light on the Islamicisation process, on language interactions and on the literary production in the Il-Khanate. Surprisingly, he explains that Ibn Al-Fuwati keeps silent about the role of important and typical figures of the conversion of the Mongols to Islam, in particular on the Mongol rulers. Conversely, the example of Mu‘izz al-Din Rukn al-Islam, the founder of a khanqah, of a madrasa, and of a hospital for the Sufis in Hamadan, shows the interpenetration of cultures, Mu‘izz al-Din being introduced by the Majma‘ as an expert of Mongol customary law, the yasa. D. DeWeese also lingers over the need for the Mongol state to attract from Central Asia scribes and technicians of international relations. This appears clearly in the biography of Mahmud Yalawach (یلواچ) who spoke Chinese, Hindi and Arabic, and wrote in Mongolian, Uighur, Turkish, and Persian. In all, this pioneering article offers a innovative approach to the impact of Mongol times on the culture of conquered lands, revealing the innumerable resources of an unvisited primary source like the Majma‘.