Difficulties in initiating and/or maintaining sleep in combination with a high degree of suffering or impaired daily activities are the main characteristics of insomnia. The worldwide prevalence of insomnia is around 6-10%. Insomnia is a heavy burden for patients as it impairs their social, family, and occupational life, and has a highly negative impact on quality of life. In terms of disability-adjusted life years, insomnia is the 9th most important brain disorder. Moreover, insomnia is also a major risk factor for depression and anxiety disorders as well as for cardiovascular diseases and diabetes. Finally, insomnia represents a heavy socioeconomic burden, especially due to productivity losses. The two most commonly used treatments for insomnia are benzodiazepine receptor agonists (BZRA) and cognitive-behavioural therapy for insomnia (CBT-I). BZRA improve sleep continuity in short-term treatment, but tolerance and dependence are important side effects. CBT-I, by contrast, is safe and effective with large effect sizes on insomnia severity. Clinical guidelines unanimously recommend CBT-I as the first-line treatment. However, health insurance data suggests that CBT-I is not widely available in routine care and mainly offered in a few specialised research settings. As a result, patients with insomnia have limited access to first-line treatment in clinical practice. Recently, there has been growing evidence that internet-delivered CBT-I (iCBT-I) is highly effective with effects appearing to be comparable to those of face-to-face CBT-I. Consequently, iCBT-I has been suggested as a promising solution since it can be disseminated on a large scale, giving more patients access to effective treatment. In addition, it is easily accessible anytime and anywhere, fitting in with an increasingly digital lifestyle. The higher flexibility of iCBT-I may provide more convenience, patients save some of the time and costs of seeing therapists. Although there are good reasons to hypothesize that iCBT-I is an adequate alternative to face-to-face CBT-I, conclusive evidence has not yet been established. In fact, it has not been proven whether the optimism about iCBT-I as an additional first-line treatment is justified. For the first time, the planned non-inferiority study will investigate whether patients would benefit from iCBT-I to the same degree as from face-to-face interventions. So far, iCBT-I and face-to-face CBT-I have not yet been evaluated in an adequately designed non-inferiority study. In case non-inferiority is confirmed, patients can be confident that both formats of CBT-I are equally likely to reduce insomnia severity. Similarly, the study will provide solid evidence for general and sleep medicine practitioners and psychotherapists, broadening their therapeutic options. Policy-makers will gain information useful for implementing iCBT-I into routine care.