The definitions, nature, and extent of sex crimes committed against adults (rape/sexual assault and sex trafficking/prostitution) and children (sexual abuse, incest, pedophilia, and child sex trafficking) are presented. Three common explanations for sex offending are provided: feminist theory of rape, economic theory of sex trafficking, and pathological/individualistic explanations of child sexual abuse. Emerging research areas on juvenile sex offenders and female sex offenders, as well as sex offending in the contexts of the military, on college campuses, and in correctional settings (prisons, jails, juvenile confinement facilities) are presented.