Hypersomnolence, a broad presentation encompassing excessive daytime sleepiness, hypersomnia and sleep inertia, affects around 25 % of patients with a major depressive disorder. Yet, hypersomnolence is often overlook in clinical settings - which can prevent remission of the mood disorder in addition to significantly interfering with quality of life. Clinical guidelines are lacking to support clinicians in the diagnosis and treatment of hypersomnolence in depression. Pharmacological treatment with selective serotonin reuptake inhibitors is insufficient and noradrenaline and dopamine reuptake inhibitors or similar molecules are generally indicated. Low-sodium oxybate was recently approved for Idiopathic Hypersomnia, but studies are needed to assess its efficacy in patients with comorbid depression. In parallel, cognitive behavioral therapy for hypersomnia is being developed as adjunct non-pharmacological treatment. Light therapy might also be beneficial in these populations. This narrative review aims at proposing a diagnostic approach reconciliating psychiatry and sleep medicine nosologies, as well as offering a multimodal treatment algorithm for hypersomnolence in depression.