While guenons vary greatly in coloring and facial characteristics, there are certain characteristics that they have in common. Generally, the guenon is a medium to large monkey, slender in build, measuring (head and body) 13-27.5 in (32.5-70 cm). Its tail is considerably longer than its body, ranging in length from 19.5-34 in (50-87.5 cm). Guenons are most active during the day, can be either terrestrial or arboreal, and walk on four feet, sometimes with slightly lifted wrists and ankles. While their jaws are short, they have well-developed cheek pouches. These pouches allow them to forage for food in open areas and then return to shelter to chew and swallow their food.
All guenons are easily recognized by their colorful fur. They are usually grayish green on their backs and the tops of their heads, and get much lighter down their sides and on their stomachs and undersides—usually light gray to white. However, as many of their species' names indicate, their coloring varies a great deal between species. Many species have ornamentation around their heads, such as white noses, white mustaches, white beards, prominent side whiskers, white throats, and/or white or brown brow bands. Their legs can also be decorated, sometimes with white or beige stripes on their thighs or bright coloring on the insides of their legs. Furthermore, the coloring of the young is occasionally different from that of adults.
The size and territory of guenon troops varies from species to species. Some species, such as the mustached guenons, stay within fairly strict territorial boundaries. Other species do not observe these boundaries at all, and roam freely. Within guenon troops, the ranking system found with baboons is only very loosely established.
The manner in which guenons feed is closely related to their habitat. For example, arboreal guenons primarily eat leaves and tree fruit. Reportedly, guenons in the wild will also eat eggs, although this has not been verified. In their natural habitats, they eat a wide variety of foods, such as fruits and vegetables, nuts, insects, birds, lizards, and other small animals.