The sexual abuse of children is not a new phenomenon, but the traumatic short- and long-term mental health consequences make it essential to study and, ultimately, prevent. The labels for child sexual abuse (CSA) vary and have changed over time, examples being “child sexual abuse,” “child sexual assault,” “child sexual exploitation” and “unwanted sexual experiences.” Each has slightly different meanings and implications. Researchers, practitioners, criminal justice personnel, and policymakers also differ on how to define other aspects of CSA (e.g., age of the child, age differential between child and offender, what acts constitute CSA [touch or penetration only, or non-touch such as exposure to pornography], and risk factors that may become targets of prevention strategies). Such definitional debates impact all aspects of studying the concept, such as examining prevalence, assessment, and clinical interventions. Whether the perpetrators are known to the child (true in the majority of cases) or are strangers affects the length of time that the child is victimized sexually and whether and how they disclose the abuse. The sexual abuse of boys, while a relatively small proportion of sexual victimizations, was not given the attention it warranted until relatively recently. Perpetrators are both males and females (an estimated 20 percent), but the type of CSA differs based on the sex of the offender. Special circumstances in which CSA occurs include the abuse of children in institutions and the CSA of children with disabilities. Disclosing CSA is difficult for many children and, rather than directly disclosing, many mention the abuse indirectly or much later on. Once disclosed, intervention typically consists of child protection services assessment and trauma-focused counseling. Child advocacy centers (CACs) have become the standard agencies to investigate and support CSA victims and non-offending family members. There are a number of ways to provide CSA prevention programs, such as media education, but the most common approach is educating children about the risks and teaching them strategies that may assist them in avoiding abusers or seeking assistance early on. The launch of the Internet has introduced new ways to sexually abuse children, with easier access to child pornography, abuse in real time, and trafficking children for commercial sexual exploitation.