The book presents a model for happiness based on current knowledge in evolutionary biology and neurobiology. Briefly, the primary purpose of nervous systems is to direct an animal toward behaviour relevant for survival and procreation. In primitive animals actions are based on reflexes, while in humans the modules directing behaviour engage positive and negative affect (good and bad feelings), and they are swayed by cognitive processes. The reason why evolution opted for this strategy was the improved flexibility in response, i.e., we learn from previous experiences. The human capacity for happiness is an accidental consequence.In short, the book offers both a deeper understanding of what happiness is about, and a framework for improving well-being.