Temperament differs among individuals both within and between species. Evidence suggests that differences in temperament of group members may parallel differences in social behavior among groups or between species. Here, we compared temperament between three closely related species of monkey—rhesus (Macaca mulatta), long-tailed (M. fascicularis), and pigtailed (M. nemestrina) macaques—using cage-front behavioral observations of individually housed monkeys at a National Primate Research Center. Frequencies of 12 behaviors in 899 subjects were analyzed using a principal components analysis to identify temperament components. The analysis identified four components, which we interpreted as Sociability toward humans, Cautiousness, Aggressiveness, and Fearfulness. Species and sexes differed in their average scores on these components, even after controlling for differences in age and early-life experiences. Our results suggest that rhesus macaques are especially aggressive and unsociable toward humans, long-tailed macaques are more cautious and fearful, and pigtailed macaques are more sociable toward humans and less aggressive than the other species. Pigtailed males were notably more sociable than any other group. The differences observed are consistent with reported variation in these species’ social behaviors, as rhesus macaques generally engage in more social aggression and pigtailed macaques engage in more male–male affiliative behaviors. Differences in predation risks are among the socioecological factors that might make these species-typical behaviors adaptive. Our results suggest that adaptive species-level social differences may be encoded in individual-level temperaments, which are manifested even outside of a social context. Am. J. Primatol. 75:303-313, 2013. © 2012 Wiley Periodicals, Inc.