Objective: The authors reviewed studies of the effectiveness of criminal justice liaison and diversion (CJLD) services in which outcomes of participants in these services were compared with those of offenders with mental illness who received no intervention or a standard intervention. The authors synthesized existing evidence with respect to changes in mental health status or criminal recidivism. Methods: A comprehensive search (1980–2012) of more than 30 generic and specialist databases identified 6,571 published and unpublished studies. The studies, which varied considerably in methodological approach and overall quality, were systematically appraised according to Campbell-Cochrane guidelines. Ten studies met inclusion criteria. Key outcomes included a reduction in offending and postintervention changes in mental health. Results: Synthesized findings indicated that CJLD services appeared to be effective in identifying offenders with mental disorders and that participation in CJLD services had a positive impact on criminal justice and mental health outcomes. Conclusions: Although the methodologies of existing studies are only moderately rigorous, the overall findings suggest that CJLD services can be beneficial. Their effectiveness depends on the model of service delivery, the availability of community services, and the engagement of offenders with mental disorders in treatment. The successful implementation of CJLD services requires a clearer recognition of the importance of systems-of-care principles.