By definition, substance abuse refers to a pathological involvement with alcohol and/or drugs. Presence of adolescent substance abuse is largely determined by consequences of substance involvement on functioning across life domains, with the extent of involvement (i.e., quantity and frequency of use) representing a less important indicator. Problematic substance involvement by youth is most often expressed in difficulties with interpersonal relationships, increased family conflict, deterioration of academic functioning, greater levels of negative affect (e.g., depression, anxiety), and involvement in various delinquent behaviors (e.g., truancy, theft, property destruction). Adolescent substance abuse is diverse by nature, leading to difficulties in determining the direction of causality. For some teens, increased substance involvement may occur in response to difficulties (e.g., stressful life events, other psychiatric disorders), and may eventually exacerbate the original problem. For youth who have experienced few objective life difficulties, increased involvement with alcohol and other drugs may precipitate deterioration in psychosocial functioning (e.g., school problems, withdrawal and isolation, legal problems). Alternately, substance abuse may be embedded within a variety of deviant behaviors and attitudes representing a “problem behavior” syndrome (R.Jessor & S.L.Jessor, 1977).