The high prevalence rate of mental health difficulties in youth involved in the youth criminal justice system raises concerns and questions for research, policy, and practice. We examine several aspects of the intersection between mental health and youth justice policy and practice, with a particular focus on describing models of the relationship between mental health problems and justice system involvement and considering the implications of these models for the effective assessment of and intervention with justice system-involved youth. Research examining this relationship has suffered because of lack of communication between clinical and correctional researchers as well as assumptions regarding the causal role of mental health issues in offending. Recommendations following this review include widespread mental health screening for justice-involved youth, greater uptake on the available provisions for specialised assessments and sentencing for youth with mental health concerns, and a research agenda that focuses on the relationship between mental health concerns and criminal behaviour.