Today, juvenile court is experiencing the advancing use of experts, particularly mental health professionals. Recent literature suggests that mental health problems may afflict a large portion of youth in the juvenile justice system. However, expert testimony can be used to excuse the potentially dangerous and harmful behavior of youth. If juvenile court is to retain its character as a viable alternative to criminal court prosecution, the court must consistently demonstrate a unique ability to protect communities, and hold youth accountable, while helping youth become productive, responsible adults. The system must demonstrate that it is suited to deliver justice. To accomplish that goal, prosecutors must be knowledgeable about the mental health and competency issues that they face, including an understanding of the assessment and evaluation tools used by defense experts, particularly their limitations and potential for misuse. This guide, supported by the U.S. Department of Justice, Office of Juvenile Justice and Delinquency Prevention (OJJDP) is divided into three parts. Part 1 covers the basics of psychological evaluations which include a discussion of the Diagnostic and Statistical Manual on mental illness diagnosis. Part 2 addresses the emerging issue of competency to stand trial and competency to waive Miranda rights. Part 3 addresses preparation for examination of an expert witness. Appendixes 1-2 and references