Anxiety disorders are one of the most prevalent mental health problems. They are associated with considerable individual suffering and substantial economic burden. Cognitive behavioral therapy (CBT) is considered the golden standard in psychological treatment for anxiety disorders. Internet-supported CBT, that is delivered fully or partly via the Internet, is often discussed as a promising way to increase treatment availability and reduce treatment costs. Previous studies have shown the potential of Internet-supported CBT in research settings. Whether these results generalize to clinical populations, however, is unclear. The main purpose of the present thesis is to examine the acceptability, effectiveness, and cost-effectiveness of Internet-supported CBT for anxiety patients in routine outpatient clinics.