Through long-term research with bearded capuchin monkeys (Sapajus libidinosus) in Fazenda Boa Vista, Brazil, we have deepened our understanding of tool use by non-human primates. Nut cracking with tools is a skill developed through socially mediated individual learning, resulting from the availability of fruits and hard stones. Learning this skill affects the development of perception, attention, and memory. Nut-cracking on anvil sites also increases direct competition among group members, steepening the female dominance hierarchy. Finally, the use of tools to obtain nut kernels substantially increases the diet quality of these monkeys. While the tradition of nut cracking with stone tools impacts the lives of bearded capuchin monkeys in many ways, recent studies indicate that habitat anthropization is threatening this tradition. Thus, we must act to protect capuchin monkeys.