English summary: During the Abbasid period (750-820), the vast territories beyond the Amu Darya river (the Mawara'annahr), conquered by the Umayyad generals in the first half of the eighth century, entered definitively into the cultural sphere of Islam. The comparative analysis of medieval Arabic, Persian, and Chinese sources, supplemented by materials from unpublished manuscripts, as well as the latest results yielded by archaeological excavations at Samarkand, have made it possible to establish a fine-grained chronology of this turning point in the history of Central Asia. Examined in this new light are complex and irreversible processes that resulted in a changed political and religious fabric, transformations of the Sogdian and Muslim elite, and the evolution of the state's system of controlling territories on its borders, within a context of confrontations and diplomatic relations between the caliphate, the Tang empire in China, and the Turks. French description: A partir de l'epoque abbasside (750-820), les vastes territoires situes au-dela du fleuve Amu Darya (le Mawara'annahr), conquis par les generaux umayyades durant la premiere moitie du VIIIe siecle, entrent definitivement dans l'aire culturelle de l'islam. L'analyse croisee des sources medievales arabes, persanes et chinoises, completees par les donnees de manuscrits inedits, ainsi que les derniers resultats livres par les fouilles archeologiques de Samarqand permettent d'etablir une chronologie fine de cette periode charniere de l'histoire de l'Asie centrale. Sous cet eclairage nouveau sont examines les processus complexes et irreversibles qui ont abouti a un changement du cadre politique et religieux, a la transformation des elites sogdiennes et musulmanes, a l'evolution du systeme etatique de controle des pays frontaliers, dans un contexte de confrontations et de relations diplomatiques entre le califat, l'empire chinois des Tang et les Turcs.