behavior therapy or behavior modification, in psychology, treatment of human behavioral disorders through the reinforcement of acceptable behavior and suppression of undesirable behavior. The technique had its roots in the work of Ivan Pavlov, a Russian physiologist who observed that animals could be taught to respond to stimuli that might otherwise have no effect on them. B. F. Skinner developed the technique in the United States, using positive or negative reinforcers to encourage desirable behavior and punishments to discourage undesirable behavior. Behavior therapists believe that, in many cases, behaviors can be learned or unlearned through basic conditioning techniques; unlike traditional psychoanalysis, the method has little regard for the unconscious processes underlying personality disorders. Behavior therapy uses such techniques as aversive conditioning, where unwanted habits are paired with unpleasant stimuli, and systematic desensitization, where a stimulus that causes anxiety is paired with a pleasant one.