Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Disorders and disturbances of sleep are widespread and can have significant consequences for affected individuals as well as economic and other consequences for society. Sleep medicine is a medical specialty or subspecialty devoted to the diagnosis and therapy of these sleep disturbances and disorders. From the middle of the 20th century, research has provided increasing knowledge and answered many questions about sleep-wake functioning. Learn more about sleep medicine, its history and diagnostic and treatment methods in this book.