The author looks at the psychology of sexuality and its origins in the brain's cortex. She discusses how the cues for desire sometimes overshadow mere physiological cues and how they may be healthy or unhealthy. She argues that understanding the intricate neurochemical and neurostructural workings of the mind and the central and autonomic nervous systems in both men and women--and their dependence on early attunement--helps therapists and patients distinguish sexual play from predatory, trauma-inducing sexual aggression and that this distinction is crucial given the centrality of the mammalian emotional circuit of play in our brain processes, including the sexual. She discusses the dangers of mistaking forcible rape fantasy for a real-life desire and examines other fantasies and the sexual role play that fuel our sexuality. She warns of the psychological and emotional damages of isolating, nonconsenual sex. And she discusses how sexual play can provide emotional attunement, joy, and sociability to human life.