Law enforcement, lawmakers, and the public are increasingly concerned about how people with mental illness are treated within the criminal justice system. This chapter focuses on the role of public psychiatrists in the provision of timely evaluation, expertise, and care for individuals in custody—particularly for individuals with serious mental illnesses. A case-based discussion illuminates important aspects of the legal and health care challenges facing individuals at the time of arrest, arraignment, incarceration, trial, and community re-entry. The chapter discusses mental hygiene law, criminal procedure law, advocacy, and the formation of policy with an emphasis on fitness to stand trial. Appropriate diversion of individuals with mental illness from incarceration, and its role in helping these individuals to achieve recovery, is explored in detail.