Persian (/ˈpɜːrʒən/ or /ˈpɜːrʃən/), also known by its endonym Farsi (فارسی fārsi [fɒːɾˈsiː] ( listen)), is one of the Western Iranian languages within the Indo-Iranian branch of the Indo-European language family. It is primarily spoken in Iran, Afghanistan (officially known as Dari since 1958), and Tajikistan (officially known as Tajiki since the Soviet era), and some other regions which historically were Persianate societies and considered part of Greater Iran. It is written in the Persian alphabet, a modified variant of the Arabic script.
Historically there are three major periods of development within the Persian language: Old Persian, the language of the Achaemenians (650 – 350 B.C.); Middle Persian (the Parthian period c. 350 B.C. – 230 A.D. and, immediately following that, the Sassanian period c. 230 – 650 A.D.), and New Persian, which starts to take shape after the Iranian conquest by the Arabian armies in the seventh century.
New Persian, in turn, can be divided into two major periods (regardless of the dialectal/regional variations): Classical Persian and Modern Persian. Just where can we draw the line between these two periods is a matter of debate. Probably we never can. What can be suggested with some certainty, however, is that after the invasion of Iran by the Arabian armies—due to the richness of the family of the languages which we commonly know as the “Iranian” languages—it took roughly three hundred years for this new variation of Persian to be developed and used as lingua franca.