A group of distinct psychiatric disorders (including generalized anxiety disorder, panic disorder, obsessive-compulsive disorder, social anxiety disorder, and posttraumatic stress disorder) that are characterized by marked distress and impairment of functioning. Fear is an adaptive emotion that is seen in many animal species, while anxiety can be viewed as the subjective component of fear and, therefore, a normal emotion selected for by evolutionary processes. Anxiety disorders are among the most prevalent, disabling, and costly of psychiatric disorders. They are frequently underrecognized and undertreated. Fortunately, there is growing understanding of the mechanisms underlying these disorders, and a number of effective treatments are available.