Stereotypies, or repetitive and purposeless behaviors, are observed in both humans and other animals. They have been primarily studied in captive animal and clinical human populations with comparably little research devoted to understanding less severe levels of stereotypies observed in nonclinical populations of adult humans and in most captive animals. As these behaviors are sometimes associated with routine events, I explored the relationship between the predictability of anticipated events and mild stereotypies. I studied this relationship in captive rhesus macaques and a novel comparison group of adult humans from a nonclinical population. I designed two experimental paradigms, a wait paradigm and a task paradigm, to elicit stereotypic behavior in both species. I also provided participants with questionnaires about their current emotional state and individual trait differences. I found that while my manipulations of predictability did not spur differences in stereotypic behavior, both monkeys and humans performed stereotypic behavior in both the wait and task paradigms. Humans performed similar amounts of stereotypic behavior between the two paradigms and individual amounts of stereotypic behavior were positively correlated between paradigms. Yet, the rhesus macaques performed significantly more behaviors during the wait paradigm than in the task paradigm and their stereotypic behaviors between paradigms were not positively correlated, which suggests that they responded differently to the two scenarios. I then compared monkey and human stereotypic behavior during the wait paradigm that was a 5-minute uninterrupted period for both species. The human participants performed significantly more stereotypic behavior than the captive rhesus macaques—a highly unexpected result given that there has been little research devoted to stereotypies in nonclinical adult humans. One reason for this difference may be differences in typical stimulation levels between species as participants who reported feeling more bored performed more stereotypies. My results suggest that while stereotypies in captive animals are typically considered abnormal pathological behaviors that warrant intervention and mitigation, they may serve a function in response to the current environment that is retained across two species of primates. As intervention and mitigation are typically not proposed for mild levels of stereotypic behavior in nonclinical populations of humans, the results in this dissertation suggest that captive animal managers may need to reexamine management strategies for captive animals that perform mild levels of stereotypic behavior.