Abstract: [The Concept of Romania in Western and Byzantine Literary Sources (4th to 15th centuries)]. Our study aims to analyse the definitions and historical significances of the concept of Romania. The term Romania is found for the first time in Latin writings from the 4th century. Here, it designates the Roman Empire and its civilisation, as opposed to the territory occupied by the barbarians (Barbaricum). During the last quarter of the 4th century, the political unity of the Roman Empire (Romania) is doubled by a unity of faith, as the Empire becomes officially Christian. The limits of the Christian Church are the limits of the Empire itself. This unitarianism between the Church and the Empire is indicated in Latin texts by the same term - Romania, which thus receives a religious connotation. Starting with the 6th century, eastern, Greek-language writers use the term in order to designate the Eastern Roman Empire, whose capital city was Constantinople. The official title of the Byzantine state (Basileia ton Rhomaion) and the word used for the inhabitants of the New Rome (rhomaioi) reflect the idea of continuity between the Old Rome and the New (Constantinople), as well as the Byzantine citizens' belief that they were the descendants of the Romans. After the year 1080, Westerners use the term Romania to refer to the Byzantine Empire, according to Byzantine tradition. Starting with 1204, Romania designates the Latin Empire of Constantinople. In time, the concept and its derivatives received political, ethnical as well as religious connotations.