Chronic insomnia is preferably treated with cognitive behavioral therapy for insomnia (CBTI), but many insomnia sufferers receive medication instead, likely because of high costs, lack of knowledge about optimal insomnia treatment among physicians, and lack of CBTI-trained professionals in mental health care. A possible solution is to offer CBTI through the Internet: I-CBTI. I-CBTI is generally acceptable to patients and greatly improves insomnia symptoms. We review the state of knowledge around I-CBTI and its effects. CBTI’s effectiveness is influenced by treatment characteristics and patient-specific factors. We review potential factors that help identify which patients may benefit from I-CBTI.