The Illyrians were a group of tribes who inhabited part of the western Balkans in antiquity and the south-eastern coasts of the Italian peninsula. The territory the Illyrians covered came to be known as Illyria to Greek and Roman authors, corresponding to parts of the former Yugoslavia and Albania, between the Adriatic Sea in the west, the Drava river in the north, the Morava river in the east and the mouth of the Vjosë river in the south. The first account of Illyrian peoples comes from Periplus or Coastal Passage, an ancient Greek text of the middle of the 4th century BC.
These tribes, or at least a number of tribes considered "Illyrians proper", are assumed to have been united by a common Illyrian language, of which only small fragments are attested enough to classify it as a branch of Indo-European, while it was extinct by the 5th century AD. However, the name "Illyrians" as applied by the ancient Greeks to their northern neighbors may have referred to a broad, ill-defined group of peoples, and it is today unclear to what extent they were linguistically and culturally homogeneous. In fact, an Illyric origin was and still is attributed also to a few ancient italic people, such as Iapigi, Dauni and Messapi, as it is thought that, most likely, they had shored to the Peninsula, coming from the geographic "Illyria". The Illyrian tribes never collectively regarded themselves as 'Illyrians', and it is unlikely that they used any collective nomenclature for themselves. However, the name Illyrians seems to be the name of a specific Illyrian tribe, which was the first to come in contact with the ancient Greeks during the Bronze Age, causing the name Illyrians to be applied to all people of similar language and customs.
The term "Illyrians" last appears in the historical record in the 7th century AD, referring to a Byzantine garrison operating within the former province. All the remaining tribes except perhaps the Romanized Vlachs were Slavicised in the course of the Middle Ages, while modern Albanian might have descended from a southern Illyrian dialect.