Narcolepsy is widely regarded as the prototypical hypersomnia of central origin. Enormous progress has been made in our understanding of the pathophysiology of the disease, providing additional insights into mechanisms regulating normal sleep and wakefulness. At the same time, it is increasingly recognized that the clinical phenotype of narcolepsy is broad and includes nonsleep symptoms, reflecting metabolic dysfunction and disorders of emotional processing and cognition. This review focuses on the clinical aspects and diagnostic approach toward patients with narcolepsy, emphasizing the severe impact the disease has on daily life.