The Ancient Greek language is the historical stage of the Greek language as it existed during the Archaic (9th–6th centuries BC) and Classical (5th–4th centuries BC) periods in ancient Greece. The Hellenistic (post-Classic) period of Ancient Greece formally constitutes its own stage in the Greek language known as Koine Greek.

Ancient Greek is subdivided into various dialects, including the Homeric Greek of the Homeric poems, and the Attic Greek of great works of literature and philosophy of the Athenian Golden Age.

For information on the Hellenic language family prior to the creation of the Greek alphabet, see articles Mycenaean Greek and Proto-Greek.

Dialects of Ancient Greek

main: Ancient Greek dialects The origins, early forms, and early development of the Hellenic language family are not well understood, owing to the lack of contemporaneous evidence. There are several theories about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Indo-European language (not later than 2000 BC), and about 1200 BC. They have the same general outline but differ in some of the detail. The only attested dialect from this period is Mycenaean, but its relationship to the historical dialects and the historical circumstances of the times imply that the overall groups already existed in some form.

The major dialect groups of the Ancient Greek period can be assumed to have developed not later than 1120 BC, at the time of the Dorian invasion(s), and their first appearances as precise alphabetic writing began in the 8th century BC. The invasion would not be "Dorian" unless the invaders had some cultural relationship to the historical Dorians; moreover, the invasion is known to have displaced population to the later Attic-Ionic regions, who regarded themselves as descendants of the population displaced by or contending with the Dorians.

The ancient Greeks themselves considered there to be three major divisions of the Greek people, into Dorians, Aeolians, and Ionians (including Athenians), each with their own defining and distinctive dialects. Allowing for their oversight of Arcadian, an obscure mountain dialect, and Cyprian, far from the center of Greek scholarship, this division of people and language is quite similar to the results of modern archaeological-linguistic investigation. This is very important to realize because of the content and the change that has occurred.

One standard formulation for the dialects is:

West and non-west Greek is the strongest and earliest division, with the non-west in subsets of Ionic-Attic (or Attic-Ionic) and Aeolic vs. Arcado-Cyprian, or Aeolic and Arcado-Cyprian vs. Ionic-Attic. Often non-west is called East Greek.

The Arcado-Cyprian group is descended more closely from the Mycenaean Greek of the Bronze Age.