One of the hallmarks of human psychology is our species' ability to reason about the minds of other individuals, a capacity commonly referred to as a theory of mind (ToM). Although developmental studies have revealed much about ontogeny of our ToM abilities, to date, there is still much controversy concerning the evolution of these capacities and their emergence in non-human primates. I will present the results of several studies exploring what rhesus monkeys (Macaca mulatta) know about the minds of human competitors in the absence of training. These new findings suggest that monkeys may understand more about the minds of others than previously thought. Our results demonstrate that monkeys discriminate agents from non-agents, understand how barriers block visual access, and recognize what competitors can and cannot see,
hear, and know. These findings will be discussed in light of related work in developmental psychology and cognitive neuroscience.