The report summarizes the effects of psychosocial interventions for persons with dual diagnosis. More specifically the effects on substance use, mental state, functioning and quality of life were investigated for the following psychosocial interventions: integrated treatment, case management, assertive community treatment, cognitive behavioural therapy, motivational interviewing, family therapy, social skills training, self-help groups, housing care and vocational rehabilitation. The report summarizes the effects of the interventions compared to other psychosocial interventions or treatment as usual. We searched for systematic reviews based on randomized controlled trials encompassing persons over 15 years with serious mental illness and substance use disorder. The systematic reviews were included according to our inclusion criteria and quality assessments. We summarized the reported results and used GRADE to evaluate the quality of the evidence and strength of recommendations. We included two systematic reviews which reported results for seven of the ten psychosocial interventions. For motivational interviewing a positive effect on alcohol consumption compared to psychoeducative therapy was revealed. For cognitive behavioural therapy combined with motivational interviewing there was a positive effect on social functioning and life satisfaction compared to treatment as usual ( psycho-educative treatment and group discussions). As for the other interventions, there were either no statistically significant results or the quality of the evidence was very low. The results were based on single heterogeneous studies with relatively small populations and methodological limitations. We found no systematic reviews including relevant studies on the effects of family therapy, housing care and vocational rehabilitation. The systematic reviews gave no compelling evidence to support one type of psychosocial intervention over other interventions. There was some support for motivational interviewing alone or in combination with cognitive behavioural therapy. Further research is needed in order to improve the evidence in this field.