From the moment that Prussia entered the world of the crusade movement and the zone of Western European external expansion in the thirteenth century, and was quickly dominated by the Teutonic Order, the new Prussian land created by the Order became a transitional area and a frontier country. A significant aspect of Prussia’s character was ethnic diversity and a consequent multiculturalism. This collective volume takes up the subject of ethnicity in Prussia between the 13th and 16th centuries and shows several other aspects of this phenomenon in a region on the outskirts of late medieval Europe. Lithuanians arriving from the east, Poles migrating from the south and Curonians living in the north-eastern peripheries come to light, but the volume also analyseS issues of interethnic relations, both in the so-called ‘period of conquest’ (13th century) and at the turn of the Middle Ages and the Early Modern period (15th/16th centuries). Also, the issue of linguistic differentiation among the predominantly German-speaking brothers of the Teutonic Order, previously unnoticed in historiography, although difficult to grasp, is presented. Eight papers offer a new contribution to the subject of multiethnicity in late medieval Prussia. The book is partly the outcome of the panel The Multiculturalism of Prussia in the Late Middle Ages: Ethnic Groups, Elites, Ideas organised in 2022 at the Congress of Polish Medievalists in Katowice, in connection with the implementation of the research project The Historical-Geographical Dictionary of Prussia in the Middle Ages and at the Dawn of the Early Modern Period, vol. 1: Lower Prussia, vol. 2: Ermland, funded by the polish National Programme for the Development of the Humanities (no. 11H160151 84).