Forty million Americans are afflicted with chronic disorders of sleep. Sleep disorders cause 38,000 cardiovascular deaths and cost over $16 billion annually. Indirect costs of accidents, property destruction, litigation, hospitalization, and death add another $50–$100 billion. Worldwide, about 10 percent of the population meet diagnostic criteria for insomnia disorder. Obstructive sleep apnea (OSA) is becoming more ubiquitous as the obesity epidemic enhances risk for OSA. Recurrent episodes of not breathing (apnea) or reduced airflow (hypopnea) during sleep leads to an almost constant daytime state of a brain starved for oxygen. It is likely that some 10 percent of the general population has OSA but that is probably a low estimate given that OSA is likely severely underdiagnosed, particularly among African Americans, overweight individuals, and older adults. Sleep disorders also carry huge consequences for mental health. For example, 65–90 percent of adults with major depressive disorder (MDD) report sleep problems, and 90 percent of children with depression report disturbed sleep. It is not just that sleep problems result from mental health problems, sleep problems can precipitate or help cause mental problems.