The Altai Mountains (//; also spelled Altay Mountains; Altay: Алтай туулар, Altay tuular; Mongolian: ᠠᠯᠲᠠᠢᠶᠢᠨ ᠨᠢᠷᠤᠭᠤ, Altai-yin niruɣu (Chakhar) or Алтайн нуруу, Altain nuruu (Khalkha); Kazakh: Алтай таулары, Altai’ tay’lary, التاي تاۋلارى; Russian: Алтайские горы, Altajskije gory; Chinese: 阿尔泰山脉, Ā'ěrtài Shānmài, Xiao'erjing: اَعَرتَىْ شًامَىْ; Dungan: Артэ Шанмэ) are a mountain range in Central and East Asia, where Russia, China, Mongolia, and Kazakhstan come together, and are where the rivers Irtysh and Ob have their headwaters. The northwest end of the range is at 52° N and between 84° and 90° E (where it merges with the Sayan Mountains to the east), and extends southeast from there to about 45° N and 99° E, where it gradually becomes lower and merges into the high plateau of the Gobi Desert.
The name "Altai" means "Gold Mountain" in Mongolian; "alt" (gold) and "tai" (suffix – "with"; the mountain with gold) and also in its Chinese name, derived from the Mongol name (Chinese: 金山; literally: "Gold Mountain"). In Turkic languages altın means gold and dağ means mountain. The controversial Altaic language family takes its name from this mountain range.