Some monkeys prey upon insects, lizards, birds, frogs, crabs, shellfish, other small mammals and reptiles. Baboons are known to eat young antelope and rabbits when they can catch them. Most monkeys are omnivores, with diets consisting of an assortment of fruits, leaves, insects and small animals. A few monkeys are strictly herbivores, and eat only plants.

Ranging in size from about 4 1/2 inches to just over 3 feet tall, different types of monkeys can have very different features and habits. There are two groups of monkeys. Old World monkeys live in Africa and Asia. They have small, curved nostrils that are set close together. New World monkeys, which live in Mexico, Central America and South America, have nostrils that are farther apart. Some Old World monkeys have cheek pouches for storing food they'll eat later. No New World monkeys have this feature. New World monkeys have prehensile tails to grasp and hold objects, while Old World monkeys' tails are incapable of grasping.

Most monkeys live in trees, though there are some species that live on the ground. They exist in the wild, but are sometimes kept as pets. They are often used for scientific research, as sources of food or as objects of worship.