The Mongolia–Russia border is the state border between Russia and Mongolia. It is virtually all land. The total length of the border is 3485 km. The boundary is the third longest border between Russia and another country, behind the Kazakhstan-Russia border and the China-Russia border.
Most of the modern shape of the boundary was acquired in 1911 (Tuva was under Qing rule, and had declared independence in 1911 as well, with the Tuvan People's Republic declared in 1921, until being annexed into the Soviet Union in 1944), when Mongolia declared independence from the Qing Empire. Prior to that it was part of the border between the Russian and Qing Empires.
At the border there are about 20 official crossing points among them Altan - Agantsyn Gol, Tayrisin - Arshan, Bayan - Dzurh. The main problem at the Russian-Mongolian border, especially in the area of Republic of Tuva are cattle rustling and smuggling of meat.
Federal subjects of Russia bordered by Mongolia
Currently, Mongolia borders 4 subjects of the Russian Federation:
Provinces of Mongolia bordered by Russia
There are currently 8 provinces of Mongolia who border Russia: