This article describes current evolutionary research on adolescent sexual and romantic behavior. It first reviews functional explanations for basic sex differences in behavior. As in other pair-bonding mammals, women seek dominant males, and men seek and guard young, fertile females. Recent work is then described on adolescent competitiveness, mate selection, and pair bonding. The outcomes of even childhood social competition can be profound, with healthy, early-maturing, attractive children deriving lifelong benefits. Adolescent competition is intense among girls as well as boys. Depression is more common for boys with few sex partners, and for girls with many. Based on cross-cultural data and on analysis of pubertal changes in girls and boys, it can be concluded that adolescents have an evolved propensity for early sexual experimentation, followed by more judicious mate choice. Yet the bond with a girl's first sex partner is often profound. Amorous infatuations are intense in both sexes and usually mitigate within 3 years, for plausible adaptive reasons. Early menarche and unmarried motherhood impose developmental disadvantages on children but may be an evolved adaptation for stressful family conditions and a shortage of marriageable men. Gaining an understanding of normal adolescence can help in diagnosing, preventing, and treating problematic behaviors.