This review examines the role of hormones in the development of social and nonsocial cognition and the brain. Research findings from human studies designed to elucidate the effects of both prenatal and postnatal exposure to hormones in children and young adults are summarized. Effects are found to be both time and dose dependent, with exposure to abnormal hormone levels having a limited impact outside the “critical window” in development. Particular attention is given to the role of prenatal hormone exposure, which appears to be vital for early organization of the brain. In later life, measurements of circulating hormone levels and the administration of testosterone and oxytocin are found to predict behavior, but the effect is thought to be one of “activation” or “fine-tuning” of the early organization of the brain. Possible directions for valuable future research are discussed.