Major depression is highly prevalent, and is associated with high societal costs and individual suffering. Evidence-based psychological treatments obtain good results, but access to these treatments is limited. One way to solve this problem is to provide internet-based psychological treatments, for example, with therapist support via email. During the last decade, internet-delivered cognitive-behavioral therapy (ICBT) has been tested in a series of controlled trials. However, the ICBT interventions are delivered with different levels of contact with a clinician, ranging from nonexisting to a thorough pretreatment assessment in addition to continuous support during treatment. In this review, the authors have found an evidence for a strong correlation between the degree of support and outcome. The authors have also reviewed how treatment content in ICBT varies among treatments, and how various therapist factors may influence outcome. Future possible applications of ICBT for depression and future research needs are also discussed.