At first, the infant clings to its mother's underside. Later, the young monkey rides on its mother's back. All species of monkeys live together in social groups. New World monkey groups seldom consist of more than 20 members. Old World monkey groups usually have from 30 to 100 members.
Family groups consist of an adult male, an adult female, and their young.
Three Old World species may also live in family groups. They are De Brazza's guenons, Mentawi Island langurs, and Hamlyn's owl-faced monkeys. Multimale groups may consist of a number of adult males, about twice as many adult females, and their young. Most New World monkeys live in such groups, including capuchins, howlers, spider monkeys, squirrel monkeys, and marmosets. Many Old World monkeys, including langurs, macaques, and most baboons, also live in multimale groups.