The third and last group of the Indo-Iranian subfamily consists of the Iranian languages, spoken by about 95 million people, mainly in Iran, Afghanistan, Pakistan, and parts of Central Asia. Historically, the oldest Iranian forms of which there are any records are Avestan and Old Persian, both highly inflected languages. Old Persian has survived in cuneiform inscriptions from the time of the Achaemenid kings, who ruled ancient Persia during the 6th to 4th cent. B.C. Avestan is the language in which was composed the Avesta, or sacred text of the Zoroastrian religion. The Avesta probably dates from about the 7th to the 5th cent. B.C., but apparently was handed down orally and was not recorded in writing until much later. Avestan is still in use today as the liturgical language of the Zoroastrian faith. The Middle Iranian period, dating from the 3d cent. B.C. to the 9th or 10th cent. A.D., is characterized by considerable grammatical simplification, as in the reduced inflection of the noun and verb. Among the languages surviving in written records that fall within this period are Parthian, Middle Persian, Khwarazmian, Sogdian, and Saka.
The modern Iranian languages, dating from about the 9th or 10th cent. to the present, show phonetic and grammatical simplification. For example, case endings tend to be dropped and the use of prepositions substituted. The most important of the modern Iranian languages is Modern Persian (FārsĪ) the official tongue of Iran, which stems directly from Middle Persian, but has been influenced by Arabic and Turkish. It has a great literature of considerable age and is spoken by over 40 million persons in Iran and Afghanistan. There are a number of dialects of Modern Persian. Other modern Iranian languages include Pashto (also called Pushtu and Afghan), with 18 million speakers in Afghanistan, where it is the national language, and in Pakistan and Iran; Baluchi, which has about 6 million speakers, chiefly in Pakistan and Iran; Kurdish, the language of perhaps 20 million Kurds living mainly in Turkey, Iran, Iraq, and Syria; the Pamir dialects or languages, spoken in parts of Afghanistan, Pakistan, and the former Soviet Union; Yaghnobi, which is derived from Sogdian and spoken in Tajikistan; and Tajiki, a tongue of more than 5 million people in Tajikistan and Uzbekistan. Today's Iranian languages are written in adaptations of the Arabic alphabet, except for Tajiki, which uses Cyrillic characters.