Mazandarani or Mazani (مازنی), or Tabari (تبری), is an Iranian language of the Northwestern branch spoken by the Mazandarani people. , there were 2 million native speakers. As a member of the Northwestern branch (the northern branch of Western Iranian), etymologically speaking, it is rather closely related to Gilaki and also related to Persian, which belongs to the Southwestern branch. Though the Persian language has influenced Mazandarani to a great extent, Mazandarani still survives as an independent language with a northwestern Iranian origin.
Mazandarani is closely related to Gilaki, and the two languages have similar vocabularies. The Gilaki and Mazandarani languages (but not other Iranian languages) share certain typological features with Caucasian languages (specifically the non-Indo-European South Caucasian languages), reflecting the history, ethnic identity, and close relatedness to the Caucasus region and Caucasian peoples of Mazandaranis and Gilak people.
The name Mazanderani (and variants of it) derives from the name of the historical region of Mazandaran (Mazerun in Mazanderani), which was part of former Kingdom of Tapuria. People traditionally call their language Tabari, as the Tabari themselves do.
The name Tapuri / Tabari (which was the name of an ancient language spoken somewhere in former Tapuria) is now used in preference to the name Mazandarani by the young.
However, both Gilan and Mazanderan formed part of the state known as Tapuria.
The earliest references to the language of Mazandaran, called Tabari, are to be found in the works of the early Muslim geographers. Al-Muqaddasī (or Moqaisi, 10th century), for example, notes: "The languages of Komish and Gurgan are similar, they use hā, as in hā-dih and hāk-un, and they are sweet [to the ear], related to them is the language of Tabaristan, [similar] save for its speediness."
Among the living Iranian languages, Mazanderani has one of the longest written traditions, from the tenth to the fifteenth century.