The Callitrichidae includes several genera, including the marmosets, tamarins, and lion tamarins.  All callitrichids are arboreal  (tree climbers). They are the smallest primates. They eat insects, fruit, and the sap or gum from trees.

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Callitrichids typically live in small, territorial groups of about 5 or 6 animals.  This communal breeding system involves groups of multiple males and females, but only one female is reproductively active. Females mate with more than one male and everyone shares the responsibility of carrying the offspring.

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 They are the only primate group that regularly produce twins, which constitute over 80% of births in species that have been studied. Unlike other male primates, male callitrichids generally provide as much parental care as females.