Because no simple mechanism accounts for all forms of aggressive behavior, the assessment of aggression requires an examination of the context of the behavior as well as the adolescent's unique personality structure, conflicts, and behavioral response styles. The peaking of aggression during early to middle adolescence has been found in much research and appears to relate to the developmental tasks of adjusting to puberty and of furthering their own identity development. The psychological characteristics of aggressive adolescents relate to their cognitive appraisal processes, cognitive impulsivity, problemsolving mechanisms, inhibitory mechanisms, defense mechanisms, and the networks formed among the various cognitive processes. Assessment techniques include projective tests like the Rorschach and thematic apperception tests, general self-report inventories like the Minnesota Multiphasic Personality Inventory, and specific self-report inventories for aggression and anger. Other assessment techniques include measures of specific cognitive mediating processes and behavioral assessment through rating scales and behavioral research instruments. Psychological assessment is appropriate for some adolescents when used with clinical interviews. Psychological measures should be chosen and interpreted cautiously. The focus should be on the adolescents' distorted appraisal processes, defense mechanisms, defective problemsolving skills, and lack of guilt, empathy, or social perspective-taking. The least valid use of the tests is the prediction of violence. One hundred thirty-six references are listed.