This article includes information on the demographic history of Kosovo.
Prehistory and antiquity
The Dardani (; ; ) were a Paleo-Balkan tribe who lived in a region named Dardania after their settlement there. The eastern parts of the region were at the Thraco-Illyrian contact zone. In archaeological research, Illyrian names are predominant in western Dardania (present-day Kosovo), and occasionally appear in eastern Dardania (present-day south-eastern Serbia), while Thracian names are found in the eastern parts, but are absent from the western parts. Thus, their identification as either an Illyrian or Thracian tribe has been a subject of debate; the ethnolinguistic relationship between the two groups being largely uncertain and debated itself as well. The correspondence of Illyrian names, including those of the ruling elite, in Dardania with those of the southern Illyrians suggests a "thracianization" of parts of Dardania.
Roman antiquity
After the Roman conquest of Illyria in 168 BC, Romans colonized and founded several cities in the region, such as Ulpiana, Theranda and Vicianum, later incorporating it into the Roman province of Illyricum in 59 BC. Subsequently, it became part of Moesia Superior in AD 87. The region was exposed to an increasing number of 'barbarian' raids from the 4th century AD onwards, culminating with the Slavic migrations of the 6th and 7th centuries. Archaeologically, the early Middle Ages represent a hiatus in the material record. The decrease in material finds corresponds to the effects which the plague of Justinian probably had throughout the Balkans as millions of people died and many regions became depopulated. The population decrease in the Balkans partially influenced the Slavic migrations of the following centuries.
Early and High Middle Ages
The region had been part of the Roman and the Byzantium until the first major Slav raids took place in the middle of Justinian's reign. In 547 and 548 the Slavs invaded the territory of modern Kosovo, and then got as far as Durres on the Northern Albanian coast and reached all the way down to Greece.
Although the Balkans had been raided by Slavic tribes, the early Slavic settlement and power in Kosovo did not become large until the region was later absorbed into the Bulgarian Empire in the 850s, when Christianity and a Byzantine-Slavic culture was cemented in the central and eastern Balkans. This era represents the formation of most Slavic toponyms in Kosovo which reflect Old Bulgarian development. The Gorani people in Kosovo represent the last population in Kosovo which still speaks a Bulgarian/Macedonian dialect.
Following the collapse of the Bulgarian Empire, the region again became part of the Byzantine Empire after the empire fully re-established itself. It would stay under Byzantine rule for nearly two centuries until Serbian Grand Prince Stefan Nemanja, who had expanded his empire south and into Kosovo, conquered it by the end of the 12th century.
According to Serbian scholars, although Albanians lived between Lake Skadar and the Devoll river in the 1100s, Albanian migration into the plains of Metohija () commenced at the end of the century. Some of the arriving Albanians were assimilated by Serbs and Montenegrins.
According to historian Noel Malcolm the Vlach-Romanian and Aromanian languages originated in the region from Romanized Illyrians and Thracians. And was a contact zone between the Albanian and Romanian language
Vlach-Romanian and Aromanian toponyms are present in the surrounding areas, such as Surdul in Southern Serbia. Katun is a living style associated with Eastern Romance people. Katun means 'village' in the Albanian, Aromanian and Romanian languages.
When King Stefan of Dečani founded the Visoki Dečani Monastery in the 1330s, he referred to "villages and katuns of Vlachs and Albanians" in the area of the white Drin. Dečanski granted the monastery pasture land along with Vlach and Albanian katuns around the Drim and Lim rivers, which carried salt and provided serf labour for the monastery.
Dušan's Code, the legal system established in 1349, included a prohibition of intermarriage between Serbs and Vlachs The protection of Slav peasants by the Dušan's Code forced many Vlachs to migrate from Serbia.