This chapter focuses on the most important sleep disorders that are important from a polysomnographic perspective. Snoring is the most common symptom of Obstructive sleep apnea (OSA). OSA can lead to excessive daytime sleepiness (EDS), which increases the risk of motor vehicle and other accidents. The American Academy of Sleep Medicine (AASM) considers polysomnography to be routinely indicated "Standard" for the diagnosis of sleep disordered breathing. It is usually difficult to differentiate symptoms of HF from symptoms of sleep-related breathing disorders as both problems may have overlapping symptoms, such as poor sleep quality, daytime somnolence or insomnia, paroxysmal nocturnal dyspnea, and easy fatigability. The severity of OSA is determined by the number of apneas and hypopneas per hour of sleep. The obstructive sleep apnea syndrome (OSAS) is defined as five or more abnormal obstructed breathing events per hour of sleep and sleepiness.