The agile mangabey (Cercocebus agilis) is an Old World monkey of the white-eyelid mangabey group found in swampy forests of Central Africa in Equatorial Guinea, Cameroon, Gabon, Central African Republic, Republic of Congo, and DR Congo. Until 1978, it was considered a subspecies of the Tana River mangabey (C. galeritus). More recently, the golden-bellied mangabey (C. chrysogaster) has been considered a separate species instead of a subspecies of the agile mangabey.

The agile mangabey has a short, overall dull olive-grey pelage. The bare skin of the face and feet is blackish. Males are 51–65 centimeters (20–26 inches) in length and weigh about 7–13 kilograms (15–29 lb), while the smaller females are 44–55 centimeters (17–22 inches) and weigh 5–7 kilograms (11–15 lb).

Similar to other mangabeys, they are diurnal. Although generally arboreal, they do spend a significant portion of their time (12–22%) on the ground, especially during the dry season. It is typically more commonly heard than seen, and males have a loud, species-specific call that is believed to be used to space themselves out. Other calls are also used to maintain group cohesion and warn of predators. Group size can be as high as 18 members, led by a single adult male. Group meetings can be friendly and may involve exchange of members. Adult males not in groups often travel singly. My own observations of this troop in Dzanga Ndoki National Park, CAR, was quite different than the literature. We encountered a “mega-troop” consisting of over 500 individuals with many males.