Captive and field studies both provide valuable and complementary information that lead to a better understanding of a species' behavioral ecology. Here, we review studies from wild, captive, and semi-free ranging populations of squirrel monkeys (Saimiri sp.), in order to (a) provide a more current (1985–2010) review of Saimiri behavioral ecology and (b) illustrate that integrating data collected in a variety of settings is an effective approach to addressing ecological questions in primates. Captive environments, such as zoological facilities and research colonies, can be advantageous to researchers by allowing longitudinal studies of behavior and reproduction, as well as providing opportunities for gathering data on life history, because physiological and life history data are known for individual animals. Studies of field populations can provide contextual information regarding the adaptive nature of behaviors that are studied in captivity. Squirrel monkeys are small, neotropical primates that have extensively been used in captive research. As the last in-depth review of Saimiri biology was published in 1985 [Rosenblum & Coe, The squirrel monkey. New York: Academic Press], we review studies since conducted on Saimiri ecology, life history, social behavior, reproduction, and conservation. Our review indicates that there is much variation in socioecology and life history traits between Saimiri species and, surprisingly, also between populations of the same species studied at different locales. In addition, much is known about squirrel monkey reproductive physiology, basic ecology, and vocal communication, but data are still lacking in the fields of life history and some adaptive components and social behavior. In particular, longitudinal studies in the field would be particularly relevant for a genus with a slow life history such as Saimiri. Finally, few data (captive or wild) are available on S. ustus and S. vanzolinii, though at least one of these species is threatened. Am. J. Primatol. 73:607–622, 2011. © 2011 Wiley-Liss, Inc.