The Tham-Lanna script (literally, the Lanna script for writing religious texts) was first used in the Lanna Kingdom, which was established by King Mangrai in the 13th century. A hypothesis exists that the script was derived from the Old Mon script of the Haribhunjaya Kingdom in the 12th century. However, as recently reported, the oldest Tham-Lanna inscription reveals that the Tham-Lanna script was first used starting at least in the 15th century, and it has been used until today. Generally, the script is used to write in Pali and northern Thai dialects in order to record various stories such as Tipitaka texts, classical literature, legal texts and medical texts. Two aspects of cultural diversity are hidden in the Tham-Lanna script: 1) the script of the Mon ethnic group has been modified in terms of forms and orthography by Tai ethnic groups so that they can write and record their stories; and 2) the Tham-Lanna script has been used by a number of Tai ethnic groups, such as Tai Yuan, Tai Lue and Tai Khuen. These Tai ethnic groups believe in Buddhism and use the Tham-Lanna script to convey their Buddhist beliefs and to express ethic identity.

In Thailand, the Tham-Lanna script was used continuously since at least the 15th century until the early 19th century, and then the script became unpopular due to the »Use Thai Alphabet« campaign, which promoted the use of modern Thai script instead of the Tham-Lanna script. However, local communities in northern Thailand have recently launched campaigns to revitalise the use of Tham-Lanna script in daily life in order to express their Lanna identity. Nevertheless, we found that a number of texts written in Tham-Lanna script today are wrong in terms of traditional orthography. The mistakes can be seen as misunderstandings of traditional orthography due to the influence of modern Thai orthography. The recent, incorrect interpretations of orthography merely aim to express Lanna identity to anyone who sees the script. These individuals will know that this script is representative of the history and prosperity of Lanna culture.