Proper care of callitrichids (marmosets and tamarins) requires a thorough understanding of the natural history, nutritional requirements, and husbandry requirements of these small delicate monkeys. This article provides information to formulate appropriate diets, to bottle-feed a rejected infant, to learn normal behaviors, to give an overview of nutritionally related diseases and treatments, provide information about husbandry, and to provide an overview of infectious diseases. Veterinarians will be better able to assist callitrichid owners in their proper care with the information provided in this article.