Polysomnography (PSG) is an essential tool for diagnosis of a variety of sleep disorders. The results of PSG should be interpreted in the context of a patient’s history and medications and observation in the sleep laboratory. As new technologies evolve, it is expected that the field will evolve. Further work is needed to determine if computerized scoring, with or without human revision, may reliably replace visual scoring in normal and abnormal sleep. Improved techniques to measure and quantify sleep itself will allow for more meaningful assessment of sleep disruption that can lead to the recognition of new disorders and better predictions of the outcomes of these disorders.