This paper reports the method and results of a systematic review of the international literature on psychological interventions with adult sexual offenders and those showing abusive sexual behaviours. It provides the results of quasi-experimental and qualitative research in this area and is linked to our previous paper in this volume (a meta-analysis of randomised control trials). The research shows that 21 studies which used quasi-experimental methodologies met the criteria for inclusion. Of these, seven studies found significant effects and 10 revealed no significant effects. As with the review of the experimental literature, there is little consensus on the capabilities of interventions from varying theoretical backgrounds in altering offenders' behaviour or attitudes. In the review of the qualitative literature, the research team identified four studies which met the Cochrane guidelines for inclusion. Valuable findings from the studies include crucial contextual information on the barriers to and facilitation of effective treatment. Three process evaluations were found; in two of these data were analysed using grounded theory, and one exploratory study was found which used thematic content analysis. However, no large process evaluations of interventions were found of sophistication or complexity, suggesting a paucity of sound qualitative research in the area. The paper concludes by suggesting the implications of this for policy-makers and practitioners working with this group of offenders.