Tamarins have rounded jaws, while the jaws of marmosets are V-shaped, with enlarged incisors. They live in a variety of forest habitats, and are primarily fruit eaters. They'll also feed on seeds, exudates, nectar, and animal prey. Though a couple of species will come to the ground for prey, most rarely leave the trees. Most are territorial, with some actively patroling their borders.
Group size is normally small.
Tamarins have been found in association with cebids, marmosets, and other tamarins. Some will respond to the alarm calls of other tamarins. There is still much to be learned, with field studies lacking for a couple of species. Most seem to have a breeding and birth season. Twins are the norm, though single births and triplets are sometimes seen.