Anxiety disorders are the most common mental disorders among adults in the United States, with lifetime and 12-month prevalences of 29% and 18%, respectively (Kessler et al. 2005a). Most persons with anxiety disorders experience significant impairment in role functioning (Kessler et al. 2005b), and costs have been estimated at more than $42 billion per year, including lost productivity, mortality, and treatment costs (Greenberg et al. 1999). Increasing numbers of people with anxiety disorders are seeking treatment (Olfson et al. 2004), although first treatment contact is still typically delayed more than 10 years after onset of the disorder (Wang et al. 2005).