Normal sleep consists of 4-5 sleep cycles including light-, deep- and rapid eye-movement sleep. Restoration of physical and psychological function are the main effects of sleep. In most cases, disturbances of normal sleep become clinically evident as problems of initiating and maintaining sleep and/or as increased daytime sleepiness. Approximately 10% of adults suffer from pronounced insomnia, a similar percentage from markedly increased daytime sleepiness. Sleep disorders cause high socio-economic costs due to increased accident risk, cardiovascular sequelae and sick leave. Most of the 88 distinct diagnoses summarized in the international classification of sleep disorders can be differentiated and managed according to patients history. In patients with severe daytime sleepiness - sleep disordered breathing being the most frequent cause - the diagnostic evaluation and treatment in the sleep laboratory is required. Effective therapeutic strategies are available for many sleep disorders. According to the underlying disorder, treatment includes a variety of measures like life style changes, differentiated medical treatment and the use of nasally applied positive pressure in patients suffering from sleep disordered breathing.