The Altai Mountains, also spelled Altay Mountains, are a mountain range in Central Asia and Eastern Asia, where Russia, China, Mongolia, and Kazakhstan converge, and where the rivers Irtysh and Ob have their headwaters. The massif merges with the Sayan Mountains in the northeast, and gradually becomes lower in the southeast, where it merges into the high plateau of the Gobi Desert. It spans from about 45° to 52° N and from about 84° to 99° E.

The Irtysh is a river in Russia, China, and Kazakhstan. It is the chief tributary of the Ob and is also the longest tributary river in the world.