The 'Phags-pa script, called hor gsar yig in Tibetan and dörbelǰin üsüg in Mongolian, is named for its creator, the Tibetan sage 'Phags-pa Lama. 'Phags-pa was appointed 'National Perceptor' in 1264 by the emperor Khubila Khan, by whom he was ordered to devise a script in which all the languages of his empire - including Tibetan, Uyghur, Mongolian and Chinese - could be written. The new script met with limited success and only scanty accounts of its creation exist in the biographies written by 'Phags pa's disciples. Until the 1980s the bulk of research into the 'Phags-pa script was done outside of the old Mongol Empire and the script was thought to have enjoyed very limited use. However in the last twenty years there has been an increase in research into the script in China and Mongolia, which has uncovered more material than was previously thought to exist. Even taking these new discoveries into account, it still appears that 'Phags-pa use was sporadic.

The shapes of the letters were based in part on Tibetan dbu can letters. There are forty-one letters used for writing 'Phags-pa. The script is an abugida; each letter represents either an independent vowel or a CV syllable having the inherent vowel /a/. Post-consonantal vowels other than /a/ are written using diacritics written linearly after (that is, below) the preceding consonant.

There are two versions of the script, one for writing texts and one for use on seals.