to Intraindividual Variation of Primate Behavior -- The Costs and Benefits of Behavioral Flexibility to Inclusive Fitness: Dispersal as an Option in Heterogeneous Regimes -- Primate Signatures and Behavioral Flexibility in Heterogeneous Regimes -- Social Cognition and Behavioral Flexibility: Categorical Decision-Making as a Primate Signature -- Female Primates as "Energy-Maximizers" in Heterogeneous Regimes -- Male Primates: "Time-Minimizers" in Heterogeneous Regimes -- Intersexual Interactions in Heterogeneous Regimes: Potential Effects of Antagonistic Coevolution in Primate Groups -- Sociosexual Organization and the Expression of Behavioral Flexibility -- Behavioral Flexibility: Interpretations and Prospects. Some 50 years ago, researchers started a study on the behavior of Japanese macaques on the islet of Koshima near Japan (Kawai, 1965). To give the monkeysanincentivetoemergefromtheforestontothebeachtheyprovided sweet potatoes and occasionally some wheat. In 1953, a young female called Imo started washing these sweet potatoes in water before eating them. This novel behavior was soon adopted by other members of the troop and spread through the population. When Imo was four years old, she discovered that by throwingamixofwheatandsandintheseashecouldseparatethegrainsfrom theunwantedsand.Again,thebehaviorwasimitatedbyothergroupmembers and,afterafewyears,mostmonkeyspracticedthismethodofobtaininggrains. This well-known example of innovative behavior and its cultural tra- mission was one of the ?rst to document primate behavioral ?exibility in the ?eld. It is not only in their foraging behavior that monkeys and apes display the most complex arrays of behaviors. For instance, Goodall's work in Gombe (e.g., van Lawick-Goodall, 1968) revealed many examples of behavioral p- terns that never failed to surprise ?eld researchers and the interested public alike.Onlyourownspeciessurpassesotherprimatesinexhibitingsuchalarge repertoire of ?exible responses in heterogeneous environments, a factor that certainly contributed to our ability to occupy almost any habitat. This striking similarity in the ability to show ?exible behaviors makes primates, incl- ing humans, the most fascinating study subjects for students and researchers. Suchaperspectiveisre?ectedinthisbook,whereJonesoutlinesthedifferent facets of primate behavior and shows that ?exibility is a hallmark of primate behavioral patterns.