Chlorocebus is a genus of medium-sized primates from the family of Old World monkeys. Six species are currently recognized, although some people classify them all as a single species with numerous subspecies. Either way, they make up the entirety of the genus Chlorocebus.

Confusingly, the terms "vervet monkey" and "green monkey" are sometimes used to refer to the whole genus Chlorocebus, though they also refer more precisely to species Chlorocebus pygerythrus and Chlorocebus sabaeus, respectively, neither of which is the type species for Chlorocebus. This article uses the term Chlorocebus consistently for the genus and the common names only for the species.

The native range of these monkeys is sub-Saharan Africa from Senegal and Ethiopia south to South Africa. However, in previous centuries, a number of them were taken as pets by early Caribbean settlers and slave traders, and were transported across the Atlantic Ocean to the Caribbean islands. The monkeys subsequently escaped or were released and became naturalized. Today, they are found on the West Indian islands of Barbados, Saint Kitts, Nevis, Anguilla, and Saint Martin. A colony also exists in Broward County, Florida.

The classification of the Chlorocebus monkeys is undergoing change. They were previously lumped together with the medium-sized arboreal African monkeys of the guenon genus, Cercopithecus, where they were classified as a single species, Cercopithecus aethiops. More species and subspecies are expected to be identified as scientists study this genus further.

The most basal member of the genus is thought to be the dryas monkey (C. dryas), which was previously classified in Cercopithecus and may potentially warrant its own genus.

The dorsal fur of Chlorocebus monkeys varies by species from pale yellow through grey-green brown to dark brown, while the lower portion and the hair ring around the face is a whitish yellow. The face, hands, and feet are hairless and black, although their abdominal skin is bluish. Males have a blue scrotum and red penis. The monkeys are sexually dimorphic, wild adult males range from 42 to 59 cm (17 to 23 in) and females are 30 to 49.5 cm (11.8 to 19.5 in), including a tail measuring 30 to 50 cm (12 to 20 in). Males weigh from 3.9 to 8 kg (8.6 to 17.6 lb) and females weigh from 3.4 to 5.3 kg (7.5 to 11.7 lb).

Unlike the closely related guenons, Chlorocebus species are not primarily forest dwellers. Rather, they are semi-arboreal and semi-terrestrial, spending most of the day on the ground feeding and then sleeping at night in the trees. However, they must drink each day and are dependent on water, so they are never far from rivers or lakes. Like most other Old World monkeys, they have cheek pouches for storing food. They are diurnal, and are particularly active in the early morning and in the later afternoon or early evening.

Chlorocebus monkeys live in multiple male/multiple female groups, which can be as large as 76 individuals. The group hierarchy plays an important role: dominant males and females are given priority in the search for food, and are groomed by subordinate members of the group. They exhibit female philopatry, a social system whereby the females remain in the same home range where they were born, and males leave once sexually mature. These monkeys are territorial animals, and a group can occupy an area of approximately .06 to 1.78 km² (0.023 to 0.687 sq mi). They use a wide variety of vocalizations. They can with warn off members of other groups from their territory, and they can also warn members of their own troop of dangers from predators, using different calls for different predators. Monkeys scream when they are disciplined by members of the troop. Facial expressions and body posturing serve as additional communication tools. Their social interactions are highly complex. Where alliances can be formed for benefit, deception is sometimes used. Physical affection is important between family members.