Children and adolescents generally enter the juvenile justice system as a result of externalizing behavior problems. Several areas of neuropsychological function have been the focus of studies of adolescent delinquency, and deficits in two areas, namely, executive functioning and verbal ability, have been associated with delinquency. Furthermore, preschoolers with co-morbid attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) were more likely to have verbal deficits than those with ODD alone. Some researchers have identified neuropsychological profiles associated with patterns of recidivism among adolescent delinquents. This chapter presents an overview of some of the most common instruments used to assess intelligence, cognition, executive function, academic achievement, personality, and behavior. All of the measures described have normative data based on national samples, and are published measures. It presents a few examples of each type of measure. The chapter also talks about personality questionnaires and behavioral questionnaires.