The country includes one of Asia's largest freshwater lakes (Hovsgol Nuur), many salt lakes, marshes, sand dunes, rolling grasslands, alpine forests, and permanent montane glaciers. Northern and western Mongolia are seismically active zones, with frequent earthquakes and many hot springs and extinct volcanoes.

The rivers drain in three directions: north to the Arctic Ocean, east to the Pacific, or south to the deserts and the depressions of Inner Asia. Rivers are most extensively developed in the north, and the country's major river system is that of the Selenge-Moron, which drains into Lake Baykal. Some minor tributaries of Siberia's Yenisey River also rise in the mountains of northwestern Mongolia. Rivers in northeastern Mongolia drain into the Pacific through the Argun and Amur (Heilong Jiang) rivers, while the few streams of southern and southwestern Mongolia do not reach the sea but run into salt lakes or deserts.