This review of current research shows there is little information in the social work literature about effectively serving the growing population of sex offenders. Social workers have a limited understanding of sex-offender characteristics, the etiology of sexually deviant behaviors, how to design effective treatment programs, or how to measure treatment outcomes. The first section of this article reviews the research literature on the characteristics of sex offenders, which is a legal term based on the commission of illegal sex-related acts. A national study of over 60,000 sex offenders found that the majority were male (96 percent), but female offenders were the most prevalent in assaults against victims under 6 years old. A separate section of the article addresses the characteristics of juvenile sex offenders, the majority of whom have themselves been sexually abused. The sociocultural characteristics of sex offenders (race and socioeconomic class) are also discussed. The article’s review of the theories of etiology for sex offenders addresses the factors related to a person becoming a sex offender. Currently, behavioral and cognitive theories are the most prominent approaches in trying to understand sex offenders. Behavioral theories are applied in understanding how deviant sexual arousal is conditioned and how poor social skills or interpersonal relationship skills undermine the maintenance of healthy intimate relationships. Cognitive theory is used to explain how thinking errors or cognitive distortions are formed and become fixed. Other sections of the article report on research reviews of the assessment of sex offenders, domains of intervention, and outcome studies. 1 table and 56 references