Lake Baikal is a rift lake located in southern Siberia, Russia, between Irkutsk Oblast to the northwest and the Buryat Republic to the southeast.

Lake Baikal is the largest freshwater lake by volume in the world, containing 22 to 23% of the world's fresh surface water. It contains more water than all of the North American Great Lakes combined. It is among the world's clearest lakes and is the world's oldest lake, at 25-30 million years. It is the seventh-largest lake in the world by surface area.

Lake Baikal formed as an ancient rift valley and has a long, crescent shape, with a surface area slightly larger than Belgium. Baikal is home to thousands of species of plants and animals, many of them endemic to the region. It is also home to Buryat tribes, who raise goats, camels, cattle, sheep, and horses on the eastern side of the lake.

The region to the east of Lake Baikal is referred to as Transbaikalia or as the Transbaikal, and the loosely defined region around the lake itself is sometimes known as Baikalia. UNESCO declared Lake Baikal a World Heritage Site in 1996.