Ancient Greek phonology is the description of the reconstructed phonology or pronunciation of Ancient Greek. This article mostly deals with the pronunciation of the standard Attic dialect of the fifth century BC, used by Plato and other Classical Greek writers, and touches on other dialects spoken at the same time or earlier. The pronunciation of Ancient Greek is not known from direct observation, but determined from other types of evidence. Some details regarding the pronunciation of Attic Greek and other Ancient Greek dialects are unknown, but it is generally agreed that Attic Greek had certain features not present in English or Modern Greek, such as a three-way distinction between voiced, voiceless, and aspirated stops (such as /b p pʰ/); a distinction between single and double consonants and short and long vowels in most positions in a word; and a word accent that involved pitch.
Koine Greek, the variety of Greek used after the conquests of Alexander the Great in the fourth century BC, is sometimes included in Ancient Greek, but its pronunciation is described in Koine Greek phonology. For disagreements with the reconstruction given here, see below.
Ancient Greek was a pluricentric language, consisting of many dialects. All Greek dialects derive from Proto-Greek and they share certain characteristics, but there were also distinct differences in pronunciation. For instance, the form of Doric in Crete had a digraph ⟨θθ⟩, which likely stood for a sound not present in Attic. The early form of Ionic in which the Iliad and Odyssey were composed, and the Aeolic dialect of Sappho, likely had the phoneme /w/ at the beginnings of words, sometimes represented by the letter digamma ⟨ϝ⟩, but it had been lost in the standard Attic dialect.