Abnormal psychology is the branch of the discipline that seeks to describe, explain, and predict abnormal human behavior. Naturally, a definition must precede any explanation or prediction of a phenomenon. Due to its complexity, abnormal psychologists have five criteria they use in defining a potentially abnormal behavior.

             First, abnormal lies outside the statistical norm. In looking at a bell curve, abnormality is that which strays too far from the average; it lies on the peripheries of the curve. This criterion has limitations as it does not account for valuable derivations such as genius and common but maladaptive behavior such as smoking. Secondly, something is abnormal if it deviates from cultural norms. It is important to acknowledge this as what is considered normal in one society may be judged as unacceptable in another. Emotional distress characterizes abnormality. In other words, in conjunction with the other criteria, there exist undesirable feelings such as distress, anxiety, or depression. Fourth, it is a potentially dangerous behavior. Lastly, abnormal behavior is a maladaptive one. It can be either maladaptive to oneself or to society. The former means that one has difficulty carrying out or meeting life"s demands. The latter disrupts group functioning. This criterion is the most flexible of all as it accepts non conformist behavior that is not harmful to oneself. Furthermore, it considers the term abnormal in a relative manner, dependent upon one"s life and circumstances.

             There are differing approaches to abnormal behavior. Behavioral and psychodynamic perspectives are common ones. Behavioral models perceive abnormality as the development of maladaptive behavior patterns. Behaviorists seek to remedy the problem by non-reinforcement of negative behaviors and positive reinforcement of desirable ones. While behaviorists have no interest in the cause of abnormal behavior, psychodynamic therapists view it as a crucial component in the healing process.