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/, as in English "bot, spot, pot"); 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.
Attic Greek had about 15 consonant phonemes: nine stop consonants, two fricatives, and four or six sonorants. Modern Greek has about the same number of consonants. The main difference between the two is that Modern Greek has voiced and voiceless fricatives that developed from Ancient Greek voiced and aspirated stops.
In the table below, the phonemes of standard Attic are unmarked, allophones are enclosed in parentheses. The sounds marked by asterisks appear in dialects or in earlier forms of Greek, but may not be phonemes in standard Attic.