a developmental course which parallels that of normal fears, with separation anxiety and simple phobias appearing in early childhood, while social anxiety, panic disorder, and agoraphobia—which often occurs secondary to panic disorder—have their onset in adolescence, along with generalized anxiety. Biological theories of anxiety implicate dysregulations of a number of systems—notably the GABA system, the adrenergic-noradrenergic system and the serotonergic system—in the etiology of anxiety. Benzodiazepines and serotonin reuptake inhibitors have been shown to partially rectify these difficulties and lead to symptomatic relief. Psychoanalytic theories implicate the defence mechanism of displacement in some anxiety disorders and undoing in OCD. Cognitive-behavioural theories of anxiety point to the role of conditioning and socialization processes in the development of anxiety disorders. Family systems theories highlight the roles of family belief systems and interaction patterns in the development and maintenance of anxiety disorder and the significance of family lifecycle transitions in precipitating the onset of these conditions. In clinical practice many clinicians take an integrative approach to assessment and treatment of anxiety disorders.