Since January 2005, the EthoCebus research project studies the behavior and ecology of wild bearded capuchin monkeys (Cebus libidinosus) in Piaui, Brazil, living in cerrado habitat (open woodland). These monkeys routinely use stones to pound open palm and other hard fruits they have placed on stone and wood anvils, in a form similar to that observed previously in only one other species of nonhuman primates in the wild: the chimpanzees of western Africa. The EthoCebus project opens a new opportunity for comparative study of complex tool use in wild nonhuman primates. We aim to understand the nut-cracking behavior of these monkeys in ecological, developmental, social, physical, and historical context. A spectrum of research projects on these topics are under way or planned by members of the EthoCebus Research Team.