The Azerbaijanis, a Turkic-speaking ethnic group living mainly in northwestern Iran and the Republic of Azerbaijan, commonly referred to as Azeris/Āzarīs or Azerbaijani Turks, also live in a wider area from the Caucasus to the Iranian plateau.

The Azeris are predominantly Shia Muslim and have a mixed heritage of Turkic, Caucasian and Iranic elements.Despite living on two sides of an international border since the treaties of Gulistan (1813) and Turkmenchay (1828), after which Iran loses its then northern territories to Russia, the Azeris form a single ethnic group.

However, northerners and southerners differ due to nearly two centuries of separate social evolution in Russian/Soviet-influenced Azerbaijan and Iranian Azarbaijan.

The Azerbaijani language unifies Azeris, and is mutually intelligible with Turkmen, Qashqai and Turkish (including the dialects spoken by the Iraqi Turkmen), all of which belong to Oghuz, or Western, group of Turkic languages.

Following the Russian-Persian Wars of the 18th and 19th centuries, Persian territories in the Caucasus are ceded to the Russian Empire and the treaties of Gulistan in 1813 and Turkmenchay in 1828 finalize the borders with Russia and Iran.

The formation of Azerbaijan Democratic Republic in 1918 establishes the territory of the Republic of Azerbaijan.