The Tian Shan (Chinese: 天山 ("celestial mountains"); Pinyin: Tiān Shān; Uyghur: تەڭرىتاغ Tengri Tagh), also commonly spelled Tien Shan, is a mountain range located in Central Asia. The Chinese name for Tian Shan or Tien Shan, may in turn go back to a Xiongnu name, qilian (祁连) reported by the Shiji as the last place where they met and had their baby as in of the Yuezhi, which has been argued to refer to the Tian Shan rather than to the range 1,500 km further the east now known by this name. A nearby mountain range, the Tannu-Ola Mountains (Tuvan: Таңды-Уула Tangdy-Uula), also bears a synonymous name ("heaven/celestial mountains" or "god/spirit mountains").

The range lies to the north and west of the Taklamakan Desert in the border region of Kazakhstan, Kyrgyzstan and the Xinjiang Uyghur Autonomous Region of western China. In the south it links up with the Pamir Mountains. It also extends into the Chinese province of Xinjiang and into the northern areas of Pakistan, where it joins the Hindu Kush.

In Western cartography, the eastern end of the Tian Shan is usually understood to be just west of Ürümqi, while the range to the east of that city is known as the Bogda Shan. However, in Chinese cartography, from the Han Dynasty to the present, the Tian Shan is also considered to include the Bogda Shan and Barkol ranges.