The skin of part of the face in some forms is blue or violet. Guenons are also quite variable cranially. Cheek pouches are present. Guenons may be characterized by having a roundish head, a slender body, long hind limbs, and a long tail. The nostrils are close together, a beard is often present, and the side whiskers are well developed.
Guenons inhabit forests, woodlands, and savannahs, usually near rivers and streams.
Some forms spend nearly all of their time in trees, jumping from one tree to another. The tail in young guenons is prehensile, but adults normally use the tail as a balancing organ. Some guenons, such as C. aethiops, often run about on the ground. This species is also a good swimmer. All guenons take shelter in trees when alarmed, however, and C. aethiops may even gather and hold well-leaved branches around itself.