Prior to the discussion of the research, the article considers some of the methodological problems that contribute to the difficulty in finding significant effect sizes in the sexual offender treatment literature, which in turn fuels the debate regarding treatment effectiveness. The authors then turn to evaluations of individual programs, namely, the California Sexual Offenders Treatment Evaluation Program, the Regional Treatment Center Sexual Offender Treatment Program, and the Clearwater Sexual Offender Treatment Program. This is followed by a review of meta-analyses of the treatment of sexual offenders. The results of three recent meta-analyses indicate that current sexual offender treatment programs produce significant reductions in both sexual and general recidivism. The authors then turn to an identification of factors discussed in the literature that affect treatment results (responsivity factors). They note that the responsivity principle states that "service delivery should be matched to the learning style of the offender." A number of factors determine what the offender's learning style will be. These include "external" responsivity factors, i.e., factors that exist outside individuals but impact their ability to benefit from treatment (e.g., therapist characteristics and setting characteristics) and "internal" responsivity factors (e.g., psychopathy and motivation). This review concludes that responsivity issues in the treatment of sexual offenders are a relatively unexplored area, that failure to address such factors can reduce the effectiveness of treatment delivery, that responsivity factors in the target population must be identified and addressed, and that further research is required. 1 figure and 131 references