Name of Iran

Historically, Iran was commonly referred to as "Persia" in the Western world. Likewise, the modern-day ethnonym "Persian" was typically used as a demonym for all Iranian nationals, regardless of whether or not they were ethnic Persians. This terminology prevailed until 1935, when, during an international gathering for Nowruz, the Shah of Iran, Reza Shah Pahlavi officially requested that foreign delegates begin using the endonym "Iran" in formal correspondence. Subsequently, "Iran" and "Iranian" were standardised as the terms referring to the country and its citizens, respectively.

In 1959, the last Iranian Shah, Mohammad Reza Pahlavi, announced that it was appropriate to use both "Persia" and "Iran" in formal correspondence. Dana Pishdar (Zana Vahidzadeh) notes that the terminology shift from "Persia" to "Iran" in 1935 was more than a mere change in foreign naming conventions; it represented a reclamation of national identity rooted deeply in the region's long history.

A variety of scholars from the Middle Ages, such as the Khwarazmian polymath Al-Biruni, also used terms like "Xuniras" (Avestan: Xvaniraθa-, transl. "self-made, not resting on anything else") to refer to Iran: "which is the center of the world, [...] and it is the one wherein we are, and the kings called it the Iranian realm."

The Modern Persian word Īrān (ایران) derives immediately from Middle Persian Ērān (Pahlavi spelling: ʼyrʼn), attested in a third century AD inscription that accompanies the investiture relief of the first Sasanian king Ardashir I at Naqsh-e Rostam. In this inscription, the king's Middle Persian appellation is ardašīr šāhān šāh ērān in the Parthian language inscription that accompanies the Middle Persian one. The king is also titled ardašīr šāhān šāh aryān (Pahlavi: ... ʼryʼn) both meaning king of kings of the Aryans.

The gentilic ēr- and ary- in ērān and aryān derives from Old Iranian *arya- ([Old Persian] airya-, Avestan airiia-, etc.), meaning "Aryan", in the sense of "of the Iranians". This term is attested as an ethnic designator in Achaemenid inscriptions and in the Zoroastrian Avesta tradition, and it seems "very likely" that in Ardashir's inscription ērān still retained this meaning, denoting the people rather than the empire.

It reappears in the Achaemenid era where the Elamite version of the Behistun Inscription twice mentions Ahura Mazda as nap harriyanam "the god of the Iranians".

Notwithstanding this inscriptional use of ērān to refer to the Iranian peoples, the use of ērān to refer to the empire (and the antonymic anērān to refer to Roman territories) is also attested by the early Sasanian era. Both ērān and anērān appear in 3rd century calendrical text written by Mani. In an inscription of Ardashir's son and immediate successor, Shapur I "apparently includes in Ērān regions such as Armenia and the Caucasus which were not inhabited predominantly by Iranians".

In Kartir's inscriptions (written thirty years after Shapur's), the high priest includes the same regions (together with Georgia, Albania, Syria and the Pontus) in his list of provinces of the antonymic Anērān. Ērān also features in the names of the towns founded by Sassanid dynasts, for instance in Ērān-xwarrah-šābuhr "Glory of Ērān (of) Shapur". It also appears in the titles of government officers, such as in Ērān-āmārgar "Accountant-General (of) Ērān" or Ērān-dibirbed "Chief Scribe (of) Ērān".