Monthon were administrative subdivisions of Thailand at the beginning of the 20th century. The Thai word monthon is a translation of the word mandala, in its sense of a type of political formation. The monthon were created as a part of the Thesaphiban bureaucratic administrative system, introduced by Prince Damrong Rajanubhab which, together with the monthon, established step-by-step today's present provinces (changwat), districts (amphoe), and communes (tambon) throughout Thailand. Each monthon was led by a royal commissioner called Thesaphiban (เทศาภิบาล), later renamed to Samuhathesaphiban (สมุหเทศาภิบาล). The system was officially adopted by the 1897 Local Administration Act, after some monthon had been established and administrative details were sorted out.

Thailand is a unitary state, which means the territories are separated into central co-dependencies, with the central government deciding everything for the provinces. The kingdom is separated into multiple levels including regions, provinces, and many more. Though, formally, Thailand is separated into three levels: provinces, districts, and sub-districts, there are also informal divisions such as parimonthon, and phak. Furthermore, there are administrative divisions of the same level with different names such as the first-level divisions of the province and the special administrative region.