A variety of theorists have focused on sexual and nonsexual motivations for sex offenses, with Laws and Marshall presenting in 1990 a comprehensive and updated theory that includes a variety of learning processes, details interactions between learning experiences, and presents these in terms of a series of testable hypotheses. The assessment of sexual arousal in the laboratory setting requires a sensor or transducer, a recording system, and some type of sexual stimuli. However, measures of penile tumescence are not infallible, and responses can be faked. Therefore, erection responses should not be used as the only means of making parole, probation, or other release decisions or to determine whether someone has or has not committed a sex offense or fits the profile of an offense that has occurred. Clinical interviews and other self-report measures are also available and appear promising for use in both clinical and research situations. Although the clinical methods require refinement, clinicians and researchers now have available some well-developed and promising methods for assessing sexual interest, at least among those who admit sex offenses. Figures and 77 references