Callithrix is a genus of New World Monkeys of the family Callitrichidae, the family containing marmosets and tamarins. The genus contains the Atlantic forest marmosets. The genera Mico and Callibella were formerly considered a subgenus of the genus Callithrix. Callithrix differs from Mico in dental morphology and in geographic distribution — Callithrix species are distributed near the Atlantic coast of South America, while Mico species are distributed further inland. Callithrix differs from Callibella in these features, as well as in size, with Callithrix species being significantly larger. Callthrix species differ from the tamarins of the genus Saguinus in that Callithrix has enlarged incisor teeth the same size as the canine teeth which are used for gouging holes in trees to extract exudates.

Species included in the genus Callithrix include:

Some authorities, including Rosenberger (1981), believe that the Pygmy Marmoset, genus Cebuella, should be included within Callithrix on the basis of genetic studies, although Cebuella is significantly smaller than Callithrix.