Sex trafficking is a crime in which a commercial sex act is illegally induced by force, fraud, or coercion or in which the person induced to perform the act is younger than the age of eighteen. Accurate clinical assessment of perpetrators or victims of this crime requires an understanding of this issue. To that end, this chapter defines sex trafficking in its various forms, describes the trafficker as a sexual offender, explains the unique vulnerability of certain populations and provides conceptual frameworks for thinking about the issue.