Summary: Social learning offers individuals the opportunity to optimize decisions in complex, changing environments. I study this second inheritance system on wild vervet monkeys, using a mix of novel experimental, observational, and physiological approaches. My research shows strong social learning biases, i.e., when, what and from whom do individuals learn. Vervets attend mostly to philopatric females, while dispersing males conform to their new group habits. Furthermore, 16 years of longitudinal data on up to seven groups of vervet monkeys enable me to document the often neglected group-level behavioral variation in dietary preferences, sociality, intergroup aggression, and intersexual dominance. Such variation is best explained by cultural differences rather than environmental variation. Animal culture research improves our understanding of human evolution and may guide conservation efforts.