Iran's population increased dramatically during the later half of the 20th century, reaching about 80 million by 2016. As of 2022, Iran's population is around 86.5 million. In recent years, however, Iran's birth rate has dropped significantly. Studies project that Iran's rate of population growth will continue to slow until it stabilises above 100 million by 2050. Half of Iran's population was under 35 years old in 2012.

Greater Iran or Greater Persia, also called the Iranosphere or the Persosphere, is an expression that denotes a wide socio-cultural region comprising parts of West Asia, the Caucasus, Central Asia, South Asia, and East Asia —all of which have been impacted, to some degree, by the Iranian peoples and the Iranian languages. It is defined by having been long-ruled by the dynasties of various Iranian empires, under whom the local populaces gradually incorporated some degree of Iranian influence into their cultural and/or linguistic traditions; or alternatively as where a considerable number of Iranians settled to still maintain communities who patronize their respective cultures, geographically corresponding to the areas surrounding the Iranian plateau. It is referred to as the "Iranian Cultural Continent" by Encyclopædia Iranica.