The blue monkey or diademed monkey is a species of Old World monkey native to Central and East Africa, ranging from the upper Congo River basin east to the East African Rift and south to northern Angola and Zambia. It sometimes includes Sykes', silver, and golden monkeys as subspecies.

The golden monkey is a subspecies of the blue monkey. It is an Old World monkey found in the Virunga volcanic mountains of Central Africa, including four national parks: Mgahinga, in south-west Uganda; Volcanoes, in north-west Rwanda; and Virunga and Kahuzi-Biéga, in the eastern Democratic Republic of Congo. It is restricted to highland forest, especially near bamboo.