Anglo-Saxon missionaries were instrumental in the spread of Christianity in the Frankish Empire during the 8th century, continuing the work of Hiberno-Scottish missionaries which had been spreading Celtic Christianity across the Frankish Empire as well as in Scotland and Anglo-Saxon England itself during the 6th century (see Anglo-Saxon Christianity).
The Anglo-Saxon mission began in the last decade of the 7th century in Frisia, whence, Benedict reminded the monks he urged to come to the continental missions, their forebears had come: "Take pity on them, for they themselves are now saying, 'We are of one blood and one bone with you.'" The missions, which drew down the energy and initiative of the English church, spread south and east from there. Almost immediately the Anglo-Saxon missionaries came in contact with the Pippinids, the new dominant family in Frankish territories. The earliest monastery founded by Anglo-Saxons on the continent is Willibrord's Abbey of Echternach (698), founded at a villa granted him by a daughter of Dagobert II. Pepin II, who wished to extend his influence in the Low Countries, granted free passage to Rome to Willibrord, to be consecrated Bishop of Frisia; Norman F. Cantor singles this out as the first joint project between Carolingians and the Papacy: "It set the pattern for their increasing association in the first half of the 8th century as a result of their joint support of the efforts of the Anglo-Saxon missionaries"
Notable among these missionaries is Saint Boniface who was active in the area of Fulda (modern Hesse), establishing or re-establishing the bishoprics of Erfurt, Würzburg, Büraburg, as well as Eichstätt, Regensburg, Augsburg, Freising, Passau and Salzburg (739) further to the south-east.
Anglo-Saxon missionary activities continued into the 770s and the reign of Charlemagne, the Anglo-Saxon Alcuin playing a major part in the Carolingian Renaissance. By 800, the Carolingian Empire was essentially Christianized, and further missionary activity, such as the Christianization of Scandinavia and the Baltic was coordinated directly from the Holy Roman Empire rather than from England.