The Azerbaijanis are an ethnic groupmainly living in northwestern Iranand the Republic of Azerbaijan. Commonly referred to as Azeris/Āzarīs (آذری - Azəri) or Azeri Turks (Azerbaijani: Azəri türkləri), they also live in a wider area from the Caucasusto the Iranian plateau. The Azeris are predominantly ShiaMuslimand have a mixed heritage of Iranic, Caucasian, and Turkicelements.

Despite living on two sides of an international border since the treaties of Gulistan(1813) and Turkmenchay(1828), after which Iranlost 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 languageunifies Azeris, and is mutually intelligible with Turkmen, Qashqaiand 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 Warsof the 18th and 19th centuries, Persianterritories in the Caucasus were ceded to the Russian Empireand  the treaties of Gulistanin 1813 and Turkmenchayin 1828 finalized the borders with Russia and present-day Iran.The formation of Azerbaijan Democratic Republicin 1918 established the territory of the Republic of Azerbaijan as it is today. As a result of this separate existence, the Azeris are mainly secular in Azerbaijanand religious Muslims in Iran. Since Azerbaijan's independence from the Soviet Union in 1991, there has been renewed interest in religion and cross-border ethnic ties