Functional approaches in psychology - which ask what behavior is good for - are almost as old as scientific psychology itself. Yet sophisticated, generative functional theories were not possible until developments in evolutionary biology in the mid-20th century. Arising in the last three decades, evolutionary psychology was inspired by these developments. This field cuts across traditional subdisciplines in psychology (e.g. social, cognitive, personality, developmental, abnormal psychology, and so on). As testified by the 23 papers in this issue, evolutionary psychology today thrives as a highly integrative, cross-disciplinary, generative approach to understanding human behavior.