The hands and feet resemble those of squirrels. The thumb and big toe are not opposable. The surfaces of the hands and feet are long relative to the digits. Additionally, all of the digits except the hallux have sharp claws, not the flattened nails found in many other primates. Callitrichids use these claws to dig into the bark of trees.
Marmosets generally have triangular upper molars , and they lack the third molar found in cebids .
Otherwise, the skull of callitrichids resembles that of a small cebid or cercopithecid, with a large braincase, short rostrum, and large, forward-directed orbits. Callitrichids are diurnal and live in family groups. The general pattern of association between males and females is monogamy or polyandry, a mating system where one female has more than one mate. Females produce one to three young annually. Young are often carried on the parents' backs.