Competing conceptions of sex offenders include popular stereotypes, governed by emotional responses and erroneous beliefs; statutory concepts, which do not provide a means for clearly distinguishing sex offenders from other offenders; normative concepts, which are characteristic of dominant sociological theories of deviance; and motivational concepts, which focus on offenders' sexual motivations. A workable concept of sex offenders must consider legal definitions of offenses, but to be useful for science, it must clearly specify distinguishing characteristics of the sex offender and clearly delimit the boundaries of this class of offender. The biopsychosocial view of sex offenses holds that a person's aggressive and sexual expressions vary according to a host of factors. Some primary factors are genetic makeup; hormonal and environmental influences at critical developmental periods; developmental stage; recent health and life experiences; and the transient configuration of hormonal state, mood, thoughts, intoxication, and external events. Sex offense research has focused on epidemiological data, offense data, offender data, and offender treatment. 22-item bibliography.