Approximately 70 million people in the United States are affected by a sleep problem. About 40 million Americans suffer from chronic sleep disorders, and an additional 20-30 million are affected by intermittent sleep-related problems. However, an overwhelming majority of sleep disorders remain undiagnosed and untreated. Some of the most common ones are insomnia, restless legs syndrome, parasomnias, circadian rhythm disorders, excessive daytime sleepiness, night terrors, sleep apnea, periodic limb movement disorder, and narcolepsy. Long standing sleep disturbances can lead to nonproductive lifestyles, poor work performance, weight gain, difficulty with concentration, and social avoidance. Some disorders, like sleep apnea, can lead to even more serious problems such as high blood pressure, heart attack, and stroke. Therefore, there is an urgent need for this introduction to the subject of sleep disorders.