The taxonomy of the marmoset genus Callithrix is re-evaluated. The members of the C. jacchus group (C. aurita, C. flaviceps, C. geoffroyi, C. jacchus, C. penicillata) are considered good species. Although they produce hybrids and even double hybrids in captivity and are largely allopatric in nature, there is some range overlap between them and natural hybrids are unknown. C. aurita coelestis and C. penicillata jordani are considered valid subspecies. C. humeralifer (including C. h. humeralifer and C. h. chrysoleuca) is probably more clossly related to the C. jacchus group than to C. argentata (which includes C. a. argentata, C. a. leucippe and C. a. melanura).