Epigenetic regulation in animals induces rapid and long-lasting effects on gene expression in response to environmental changes that frequently affect animal behavior. In the last decade, accumulating studies have revealed how epigenetic regulation affects the behavior of animals, such as learning and memory, mating and courtship, the circadian sleep-wake cycle, and foraging/starvation-induced hyperactivity. In each section of this review, we discuss what we have learned from studies with mammals, mostly mouse models. We then highlight studies with Drosophila models to compare data with mouse models. Finally, we discuss several unanswered questions and future developments in this field.