Greater Iran (Persian: ایران بزرگ‎, Irān-e Bozorg) refers to the regions of West Asia, Central Asia, South Asia and Transcaucasia where Iranian culture has had significant influence. Historically, these were regions long ruled by dynasties of various Iranian empires,[note 1][2][3][4] that incorporated considerable aspects of Persian culture through extensive contact with them,[note 2] or where sufficient Iranian peoples settled to still maintain communities who patronize their respective cultures.[note 3] It roughly corresponds to the Iranian plateau and its bordering plains.[1][5] The Encyclopædia Iranica uses the term Iranian Cultural Continent for this region.[6]

The term Greater Iran, in addition to the modern state of Iran, includes all the territory ruled by Iranians throughout history, including in Mesopotamia, Eastern Anatolia, the Caucasus and Central Asia.[7][8] The concept of Greater Iran has its source in the history of the Achaemenid Empire in Persis (modern day Pars region), and overlaps to a certain extent with the history of Iran.

In recent centuries, Iran lost many of the territories conquered under the Safavid and Qajar dynasties, including Iraq to the Ottomans (via the Treaty of Amasya in 1555 and the Treaty of Zuhab in 1639), western Afghanistan to the British (via the Treaty of Paris in 1857[9] and the MacMahon Arbitration in 1905),[10] and Caucasus territories to Russia during the Russo-Persian Wars of the 19th century.[11] The Treaty of Gulistan in 1813 resulted in Iran ceding Dagestan, Georgia, and most of Azerbaijan to Russia.[12][13][14] The Turkmanchey Treaty of 1828 decisively ended centuries of Iranian control of its Caucasian provinces,[15] made Iran cede what is present-day Armenia, the remainder of Azerbaijan and Igdir (eastern Turkey), and set the modern boundary along the Aras River.[16]

On the New Year's holiday of Nowruz of 1935, the endonym Iran was adopted as the official international name of Persia by its ruler Reza Shah Pahlavi.[17] However, in 1959, the government of Mohammad Reza Shah Pahlavi, Reza Shah Pahlavi's son, announced that both "Persia" and "Iran" could officially be used.[18]