Voyeurism is the act of watching or filming another person, without his or her knowledge, engaging in a private act (e.g., undressing, having sex, toileting) to gain sexual pleasure. It is considered to be a criminal offense in many Western countries. Currently, the prevalence of voyeurism is considered to be underestimated since it is difficult both to detect and to successfully prosecute. Because voyeurism is considered to be a sexual offense, the consequences of conviction may have serious implications for offenders. This entry addresses the legal and psychological (clinical) elements of voyeurism.