The Trans-Mongolian Railway follows an ancient tea-caravan route from China to Russia and connects Ulan-Ude, on the Trans-Baikal (Trans-Siberian) railway in Russia, with the Chinese city of Jining, by way of Ulaanbaatar in Mongolia.

Other important stops are Sükhbaatar, Darkhan, Choir, and Zamyn-Üüd/Erenhot (border crossing and gauge-changing station). The line was built between 1949 and 1961. In most of Mongolia, it is single track, and in China double track. The gauge is 1,520 mm (4 ft 11 ²⁷⁄₃₂ in) in Russia and Mongolia and 1,435 mm (4 ft 8 ¹⁄₂ in) in China. There are important branches leading to Erdenet and Baganuur.