The classical Mongolian script (in Mongolian script: (ᠮᠣᠩᠭᠣᠯ ᠪᠢᠴᠢᠭ᠌) Mongγol bičig; in Mongolian Cyrillic: Монгол бичиг, Mongol bichig), also known as Uyghurjin Mongol bichig, was the first writing system created specifically for the Mongolian language, and was the most successful until the introduction of Cyrillic in 1946. Derived from Uighur, Mongolian is a true alphabet, with separate letters for consonants and vowels. The Mongolian script has been adapted to write languages such as Oirat and Manchu. Alphabets based on this classical vertical script are used in Inner Mongolia and other parts of China to this day to write Mongolian, Sibe and, experimentally, Evenki. Moreover, it has become compulsory education in Mongolia since 1994 in an effort to restore tradition and cultural practices and widely used in symbolic arts such as Calligraphy and traditional painting.

The Mongolian vertical script was developed as an adaptation of the Uyghur script to write the Mongolian language. It was introduced by the Uyghur scribe Tatar-Tonga, who had been captured by the Mongols during a war against the Naimans around 1204. There were no substantive changes to the Uyghur form for the first few centuries, so that, for example, initial yodh stood for both [dʒ] and [j], while medial tsadi stood for both [dʒ] and [tʃ], and there was no letter for [d] in initial position. Mongolian sources often distinguish the early forms by using the term Uyghurjin script Mongolian for Uyghur style script). Western sources tend to use this term as a synonym for all variations of the Mongolian script.^{[citation needed]}