The Vilyuy (Russian: Вилю́й, IPA: [vʲɪˈlʲʉj]; Yakut: Бүлүү, Bülüü, [bylyː])[citation needed] is a river in Russia, the longest tributary of the Lena.

[citation needed] In the 1950s, diamond deposits were discovered in the area, about 700 kilometres (430 mi) from its mouth.

This led to the construction of the Mir Mine, together with access roads and an airport, and the Vilyuy Dam complex to generate power needed for the diamond concentrators.

It turns towards the south and southeast in the Central Yakutian Lowland, then back towards the east, and finally enters the Lena about 350 kilometres (220 mi) downstream of Yakutsk, near Sangar.

The main tributaries of the Vilyuy are the Ulakhan-Vava, Chirkuo, Chona, Chybyda, Ulakhan-Botuobuya, Ochchuguy-Botuobuya, Tangnary [ru], Kempendyay, Tonguo and Bappagay on the right; and the Sen, Lakharchana, Akhtaranda, Ygyatta, Markha, Tyukyan, Kosmos [1] and Tyung on the left.