Greater Iran (in Persian: ایرانِ بُزُرگ‎ Irān-e Bozorg, or ایران زَمین Irānzamīn "Iranian soil" or ایران شهر Irānshahr "The Land of Iran") refers to the regions of South, West, and Central Asia that have significant Iranian cultural influence and have historically been ruled by Iranian peoples. It roughly corresponds to the territory on the Iranian plateau and its bordering plains, stretching from Iraq, the Caucasus, and Turkey in the west, to the Indus River of Pakistan in the east. It is also referred to as Greater Persia, while the Encyclopædia Iranica uses the term Iranian Cultural Continent.

The term 'Iran' is not limited to the modern state, more or less equivalent to western Iran. Iran includes all the political boundaries ruled by the Iranian including Mesopotamia and usually Armenia and Transcaucasia. In a sense the concept of Greater Iran, starts from the history that originated with the first Persian Empire or the Achaemenid Empire in Persis (Fars), and in fact is synonymous with history of Iran in many aspects. Persia lost many of its territories gained under the Safavid dynasty, including Iraq to the Ottomans (via Treaty of Amasya in 1555 and Treaty of Zuhab in 1639), Afghanistan to the British (via Treaty of Paris in 1857 and MacMahon Arbitration in 1905), and its Caucasus territories to Russia in the 18th and 19th centuries. The Treaty of Gulistan in 1813 resulted in Persia ceding Armenia, Azerbaijan, and eastern Georgia to Russia. The Turkmanchey Treaty of 1828, after the Russo-Persian wars permanently severed the Caucasian provinces from Iran and settled the modern boundary along the Aras River.