The mental disorders discussed have been defined in the DSM-IV, which contains the standards for diagnosing 16 major classes of mental illness. Only a few are covered in this chapter, however. They are mood disorders, which include depressive disorders, such as major depression and dysthymia, manic disorders, and the bipolar disorders; psychotic disorders, in which the person has an impaired sense of reality; mental retardation (an IQ of approximately 70 or below); personality disorders (11 disorders, each with its own set of diagnostic criteria); and substance abuse and dependence. The chapter also discusses suicide, techniques of assessment and diagnosis (interview, intelligence testing, and personality tests), and legal issues and mental health assessment. In addition to making referrals to appropriate mental health professionals, the correctional counselor can use his/her understanding of the assessment process and the results to assist the offender in developing better adjustment while incarcerated or on probation. Correctional counselors and staff are in a unique position to assist in the evaluation process and to use the results of that assessment. Key concepts and terms as well as discussion questions are provided.