The Byzantine Empire has seen numerous migrations of Armenians and maintained long standing relations with Armenia. The conquest of its territory in the 11th century enhances the flow of migrants. The first part of this article attempts to present the role of the Armenians—active or passive parties—in the conduct of events of the empire’s oriental border in the years 1025–1118. While the territories of the northeast are annexed and placed under direct Byzantine administration, Armenians participate in the defense against the Seljuk Turks in the region of Antioch. The key figure here is Philaretos Brachamios. The second part of this article focuses on the Armenian communities within the Byzantine Empire, in terms of location and numbers. The sources are varied but concentrate on the aristocracy, leaving in the dark lower social ranks. Finally, this article presents religious disagreements in matters of faith, which are always underlined by sources. The emperors and the ecclesiastical hierarchy try, more or less, to convert all the Armenians to the Chalcedonian faith.