Anxiety is a heightened state of vigilance associated with an awareness of threatened danger. It is so universal a phenomenon, that everyone has experienced it, from time to time, as a normal and inescapable part of life. Anxiety becomes a diagnosable disorder when it becomes excessive, inappropriate, persistent, and incapacitating. DSM-IV and ICD 10 differ in their attempts to classify different types of anxiety disorder, but most authorities agree in distinguishing three of them: generalized anxiety disorder, phobic disorders, and panic disorder. We shall follow the DSM-IV classification.