Metacognition, or awareness of one’s cognition, involves several different but overlapping cognitive abilities, such as working memory, explicit memory, monitoring, and control. These processes are guided by multiple internal or external signals, including memory signals in the case of metamemory. Primate species including apes and rhesus monkeys have demonstrated that they can respond to both internal and external signals, and like humans, these signals can be additive and fallible. In the past few decades, there have been about five dozen studies published on nonhuman animal metacognition and while robust results have been obtained, rigorous experimental paradigms have been employed, and general progress has been made, there is a still a lot we do not know. For example, there are only a few species whose metacognitive abilities have been relatively well characterized, and even in those species significant open questions remain. After an introduction, what is known and what is not known will be explored. Similarities and differences among different primate species will be highlighted. As the chapter is comparative in nature, disparities in behavioral findings across apes and monkeys, New World and Old World monkeys, as well as primates and non-primate species will be explored. The extent to which methods can or cannot be standardized across species will be discussed, with special consideration of species’ ecological niches and experimental methods typically employed. Limitations in nonhuman metacognition research will also be considered, including the fact that most metacognition studies focus on just one species. Finally, possibilities for promising future directions in research will be offered.