Primary sleep disorders constitute a significant health problem because of their relatively high prevalence and their potential to adversely affect the morbidity, mortality, and quality of life of those who suffer from them. Sleep complaints are also common in the context of many other diseases. The National Center on Sleep Disorders Research estimates that between 50 and 70 million Americans are affected by a sleep-related problem [1]. In the 2008 Sleep in America poll by the National Sleep Foundation, 65 percent of respondents reported having experienced a sleep disturbance at least a few nights a week in the prior month, and 44 percent reported sleep problems occurring every night or almost every night [2]. The most common sleep disorder—obstructive sleep apnea syndrome—which occurs in 2 percent of women and 4 percent of men over 50—h as been linked to conditions such as angina [3], cardiac arrhythmias [4], myocardial infarction [5], stroke [6], and motor vehicle crashes [7]. Importantly, treatments that can improve quality of life and decrease morbidity are available for most sleep disorders.