Mae Hong Son Province (Thai: แม่ฮ่องสอน, pronounced [mɛ̂ː hɔ̂ŋ sɔ̌ːn]; formerly called Mae Rong Son), also spelled Maehongson, Mae Hong Sorn or Maehongsorn, is one of the northern provinces (changwat) of Thailand, on the country's western border. Neighboring provinces are (clockwise from north) Shan State of Myanmar, Chiang Mai and Tak. To the west, the province borders Kayin State and Kayah State of Myanmar.
The name Mae Hong Son means "the city of three mists". It is hemmed in by the high mountain ranges of the Shan Hills and is the most mountainous province in Thailand and is occupies 13,814 square kilometres (5,334 sq mi). The province is covered with mist throughout the year and its terrain is highly suitable for the training of elephants.