The Internet is a vast international network of computers linked to each other. Users can send electronic mail quickly and easily to each other—free or at low cost. Users can also access pages of information stored as computer files on publicly available locations called Websites. The development and widespread use of electronic mail and the World Wide Web (WWW) has many implications for clinical practice, prevention, education, and research related to cognitive behavior therapy. This article presents an overview of current usage on the Internet, provides examples of how mental health professionals can use the Web to enhance practice, presents speculation about possible future applications of the Internet, and discusses major changes that may take place that would affect clinicians, researchers, and consumers of cognitive behavior therapy.