The aim of this manuscript is to describe the procedures, recommendations, findings and value of the diagnostic methods used in Sleep Disorders including questionnaires, Actigraph, Polysomnography and Multiple sleep latency test. Specific questionnaires including evaluation of sleep quality , hyper somnolence, Respiratory Sleep Disorders and Sleep-Wake rhythm are in general, used as a screening for the Sleep Disorders and indication of sleep studies. Polysomnogram and Multiple sleep latency test are considered the gold standard methods for the diagnosis of majority of sleep disorders and Narcolepsy respectively. Criteria for these disorders are reported below.