Mazandarani (مازِرونی) or Tabari (تبری) (Also known as: Mazaniki) is an Iranian language of the Northwestern branch, spoken mainly in Iran's Mazandaran, Gilan and Golestan provinces. As a member of the Northwestern branch (the northern branch of Western Iranian), genetically speaking it is rather closely related to Gilaki, and more distantly related to Persian, which belongs to the Southwestern branch.

The name Mazandarani (and variants of it) derives from the name of the historical region of Mazandaran (Mazerun in Mazandarani), which was part of former Kingdom of Tapuria. People traditionally call their language Gileki, the same as Gilekis do. Gileki consist of two morphemes : Gil + postfix ki. The name Tapuri (or Tabari) which was the name of an ancient language of somewhere in former Tapuria, Nowadays becomes prevalent into youth groups instead of Gileki. However, Gilan and Mazanderan were part of the same state known as Tapuria which its national language was known as Gileki.

Among the living Iranian languages, Mazandarani has one of the longest written traditions, from the tenth to the fifteenth century. This status was achieved during the long reign of the independent and semi-independent rulers of Mazandaran in the centuries after the Arab invasion.