Proto-Armenian is the earlier, unattested stage of the Armenian language which has been reconstructed by linguists. As Armenian is the only known language of its branch of the Indo-European languages, the comparative method cannot be used to reconstruct its earlier stages. Instead, a combination of internal and external reconstruction, by reconstructions of Proto-Indo-European and other branches, has allowed linguists to piece together the earlier history of Armenian.

Proto-Armenian, as the ancestor of only one living language, has no clear definition. It is generally held to include a variety of ancestral stages of Armenian between Proto-Indo-European and the earliest attestations of Classical Armenian.

It is thus not a proto-language in the strict sense, but "Proto-Armenian" is a term that has become common in the field.

The earliest attestation of Armenian is the 5th-century Bible translation of Mesrop Mashtots. The earlier history of the language is unclear and the subject of much speculation. It is clear that Armenian is an Indo-European language, but its development is opaque.

In any case, Armenian has many layers of loanwords and shows traces of long language contact with Anatolian languages such as Luwian and Hittite, Hattic, Hurro-Urartian languages, Semitic languages such as Akkadian and Aramaic, and Iranian languages such as Persian and Parthian. Armenian also has been influenced to a lesser extent by Greek and Arabic.

The Proto-Armenian sound changes are varied and eccentric (such as *dw- yielding erk-) and, in many cases, uncertain. That prevented Armenian from being immediately recognized as an Indo-European branch in its own right, and it was assumed to be simply a very divergent Iranian language until Heinrich Hübschmann established its independent character in 1874.

The development of voicing contrasts in Armenian is notable in being quite similar to that seen in Germanic, a fact that was significant in the formation of the Glottalic Theory. The Armenian Consonant Shift has often been compared to the famous Grimm's Law in Germanic, because in both cases, Proto-Indo-European voiceless stops became voiceless aspirates (with some complications with regard to Proto-Indo-European *p), the voiced stops became voiceless, and the voiced aspirates became voiced stops. Meanwhile, Armenian shares the vocalization of word initial laryngeals before consonants with Greek and Phrygian: Proto-Indo-European *h₂nḗr ("man", "force") renders Greek anḗr, Armenian ayr from a Proto-Armenian *aynr and Phrygian anar ("man"), which may be compared to Latin Nero and neriōsus ("strict"), Albanian njeri, Persian nar, Sanskrit nara, and Welsh nerth.

In certain contexts, the aspirated stops are further reduced to w, h or zero in Armenian: Proto-Indo-European (accusative) *pódm̥ "foot" > Armenian ոտն otn vs. Greek (accusative) póda, Proto-Indo-European *tréyes "three" > Armenian երեք erekʿ vs. Greek treis.