Several independent research groups have adapted cognitive behavioral treatments for anxiety disorders in order to deliver them via the Internet. These include treatments for posttraumatic stress disorder (PTSD), panic disorder, social phobia, and generalized anxiety disorder. In this chapter, the evidence from several randomized controlled trials is reviewed. Overall, findings suggest that Internet-delivered treatments are effective when minimal therapist support is provided via e-mail or telephone. In addition, effects tend to be close to or equivalent to face-to-face treatments. A recent development in the field of Internet treatment is to use a tailored approach in which patients are prescribed a treatment program according to their clinical profile as assessed in a structured psychiatric interview. Preliminary findings of such an approach show promising outcomes. This development may be fruitful in the treatment of PTSD as comorbidity between the different anxiety disorders is common.