Insomnia disorder is defined by difficulties initiating or maintaining sleep or waking up earlier than desired, accompanied by daytime symptoms like fatigue, impaired social or occupational performance or mood irritability. The diagnosis of insomnia disorder is solely based on taking a clinical history. A sleep laboratory investigation is only indicated when there is clinical suspicion of other sleep disorders, like sleep-related breathing disorders or sleep-related movement disorders. Clinical guidelines recommend cognitive-behavioural therapy for insomnia (CBT-I) as first-line treatment for insomnia disorder. CBT-I is a multi-component intervention comprising psychoeducation, relaxation therapy, sleep restriction therapy, stimulus control therapy and cognitive therapy. Since there is no need to complete a full psychotherapy training to use elements of CBT-I in primary care, the CBT-I components are described in this chapter to encourage healthcare professionals to use some or all of these components. According to guidelines, pharmacological treatment for insomnia should only be offered when CBT-I is not sufficiently effective or patients refuse psychotherapy. However, many patients with insomnia disorder are treated with benzodiazepines, benzodiazepine receptor agonists, sedating antidepressants or antipsychotics on a long-term basis, which is potentially harmful.