This monograph examines a wide range of evidence-based practices for screening and assessment of people in the justice system who have co-occurring mental and substance use disorders (CODs). Use of evidence-based approaches for screening and assessment is likely to result in more accurate matching of offenders to treatment services and more effective treatment and supervision outcomes (Shaffer, 2011). This monograph is intended as a guide for clinicians, case managers, program and systems administrators, community supervision staff, jail and prison booking and healthcare staff, law enforcement, court personnel, researchers, and others who are interested in developing and operating effective programs for justice-involved individuals who have CODs. Key systemic and clinical challenges are discussed, as well as state-of-the art approaches for conducting screening and assessment.