In Chapter 1, we discussed the problems encountered when describing characteristics of “normal” adolescence. These problems bear some consequence for this chapter since our view of “pathology” is that it represents a condition marked by abnormality in some structure or process. This chapter will address behaviors commonly observed in adolescents that are considered problematic by individuals who come into contact with them. Some behaviors discussed here are considered deviant because they are not prevalent in the majority of the adolescent population. Others are viewed as deviant because they conflict with societal expectations, despite their widespread prevalence among adolescents. We avoid some common technical classifications (such as the American Psychiatric Association’s classification scheme—the Diagnostic Statistical Manual [DSM-III categories]) in the present discussion because the methods necessary to arrive at these diagnoses are not always available to those in contact with adolescents. Rather, we discuss problems in the manner in which observers in the adolescent’s environment view them. We favor this approach since the expectations of the adolescent’s environment define normal and abnormal behavior; and the tolerance level of that environment is what determines whether the behavior is considered problematic enough to require intervention (Ross, 1980). Also, these are the data usually available to the practitioner.