Mae Hong Son (Thai แม่ฮ่องสอน) (also Maehongson, Mae Hong Sorn or Maehongsorn) is one of the northern provinces (changwat) 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 (also Maerongson, Mae Rong Sorn or Maerongsorn).

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.