Mae Hong Son also being called Maehongson, Mae Hong Sorn or Maehongsorn is one of the northern provinces of Thailand, and at the same time the westernmost. Neighboring provinces are (from north clockwise) Shan State of Myanmar, Chiang Mai and Tak. To the west it borders Kayin State and Kayah State of Myanmar again. It was formerly called Mae Rong Son.
Mae Hong Son (The City of Three Mists) is nestled in a deep valley hemmed in by high mountain ranges, Mae Hong Son has long been isolated from the outside world. It is the most mountainous province in Thailand and composed of a total of 13, 814 square kilometers. It is virtually covered with mist throughout the year, the name refers to the fact that this terrain is highly suitable for the training of elephants. Former governors of Chiang Mai used to organize the rounding up of wild elephants which were then trained before being sent to the capital for work. Today, Mae Hong Son is one of the "dream destination" for visitors. Daily flights into its small airport bring growing numbers of tourists, attracted by the natural scenery, numerous hill-tribe communities and soft adventure opportunities.
Most of the areas of Mae Hong Son Province are complex mountain ranges and likely still pristine virgin forest. Of the approximately 6,976,650 rai of national forest reserves, 88.02% is thought to be pristine virgin forest. Mountain ranges run unbroken from north to south with important mountain ranges being the Lao-territory mountains located on the northernmost portion of the province that serve as a boundary between Thailand and the Union of Burma and the Thanon Thongchai Mountains which are in fact three adjoining ranges, the East, West and Central Thanon Thongchai mountain ranges respectively; the West Thanon Thongchai Mountains serve as a boundary between Thailand and the Union of Burma. The mountains in the east of the province serves as the boundary between the provinces of Mae Hong Son and Chiang Mai. The tallest point is Mae Ya Peak of the East Thanon Thongchai Mountains in the Pai District in the province's northeast, at 2005 metres above sea level.