In classical and late antiquity, Illyria (/ɪˈlɪəriə/; Ancient Greek: Ἰλλυρία, Illyría or Ἰλλυρίς, Illyrís; Latin: Illyria, Illyricum) was a region in the western part of the Balkan Peninsula inhabited by numerous tribes of people collectively known as the Illyrians.

The Ancient Greeks initially used the term Illyris to define approximately the area of northern and central Albania down to the Aoös valley (modern Vjosa) and the Bay of Vlorë, including in most periods much of the lakeland area (Ohrid and Prespa). It corresponded to the region that neighboured Macedonia and Epirus. In Roman times the terms Illyria, Illyris, or Illyricum were extended from the territory that was roughly located in the area of the south-eastern Adriatic coast (modern Albania and Montenegro) and its hinterland, to a broader region stretching between the whole eastern Adriatic and the Danube.

From about mid-1st century BC the term Illyricum was used by the Romans for the province of the Empire that stretched along the eastern Adriatic coast north of the Drin river, south of which the Roman province of Macedonia began including the southern part of the traditional region of Illyria. The southeastern part, to the north of Macedonia, was organized within the province of Moesia Superior. From about 69-79 AD the province of Illyricum was subsumed into the provinces of Dalmatia and Pannonia. In the Late Roman Empire the name was used for the praetorian prefecture of Illyricum.

The region took its name from its inhabitants, the Illyrians, a group of Balkan Indo-European speaking peoples that inhabited the western part of the Peninsula in ancient times.

The earliest recorded Illyrian kingdom was that of the Enchele in the 8th century BC. The era in which we observe other Illyrian kingdoms begins approximately at 400 BC and ends at 167 BC. The Autariatae under Pleurias (337 BC) were considered to have been a kingdom. The Kingdom of the Ardiaei began at 230 BC and ended at 167 BC. The most notable Illyrian kingdoms and dynasties were those of Bardyllis of the Dardani and of Agron of the Ardiaei who created the last and best-known Illyrian kingdom. Agron ruled over the Ardiaei and had extended his rule to other tribes as well. As for the Dardanians, they always had separate domains from the rest of the Illyrians.

The Illyrian kingdoms were composed of small areas within the region of Illyria. Only the Romans ruled the entire region. The internal organization of the south Illyrian kingdoms points to imitation of their neighbouring Greek kingdoms and influence from the Greek and Hellenistic world in the growth of their urban centres. Polybius gives as an image of society within an Illyrian kingdom as peasant infantry fought under aristocrats which he calls in Greek Polydynastae (Greek: Πολυδυνάστες) where each one controlled a town within the kingdom. The monarchy was established on hereditary lines and Illyrian rulers used marriages as a means of alliance with other powers. Pliny (23–79 AD) writes that the people that formed the nucleus of the Illyrian kingdom were 'Illyrians proper' or Illyrii proprie dicti. They were the Taulantii, the Pleraei, the Endirudini, Sasaei, Grabaei and the Labeatae. These later joined to form the Docleatae.

After the Roman victory in the First Illyrian War, Illyrian Queen Teuta was forced to retreat to the Bay of Kotor, and in 228 BC the Romans imposed a protectorate on the islands of Issa and Corcyra, as well as on the cities of Epidamnos, Apollonia and Oricum. The protectorate area corresponded to the usage of the Roman concept of Illyricum.

During the Macedonian Wars, the territory of southern Illyria, which Rome had aimed to protect and control periodically for thirty years since the First Illyrian War, was involved in the conflict between Rome and Macedon. Macedon aimed to conquer, without success, the southern Illyrian ports because they would have been good bases for an attack upon Italy.