The internet is no longer something new. It has existed now for a long time and has been part of many peoples' lives for at least 20 years. The internet increasingly informs many aspects of our lives, including the economy, health care, and delivery of psychological treatments. There are many areas in which the internet has had an impact on cognitive behavioral therapy (CBT). This chapter describes challenges when delivering CBT via the internet, comments on assumptions behind treatment programs, and describes the main approaches, outcomes, and potential mechanisms of change. Further, the authors comment on the dissemination of internet-delivered CBT (ICBT), as well as applications for diverse target groups, and possible future developments. Although ICBT may appear as something new, it is almost as old as the internet itself, and the research field is very large, with more than 200 controlled trials.