This chapter examines the relationship between mental health and sexuality in humans. It considers sexual development and the psychosomatic interface between psychological processes and physiological sexual response. The chapter outlines how mental illnesses can affect sexuality and detailed specific disorders of sexuality. There are many possible ways for sexual experiences to influence our mental health, but two issues have received particular attention in recent years, homosexuality and child sexual abuse (CSA). The emergence of a homosexual identity during adolescence often leads to vulnerability in personality development. There have been various explanations for the adverse effects of CSA, although most are based on the idea that CSA is sufficiently traumatic that the adverse effects are long lasting. The interface between gender and sexuality is well illustrated by the range of gender identity problems which confront the psychiatrist.