Sleep: A Very Short Introduction addresses the biological and psychological aspects of sleep. What is sleep? Why do we need it? How much is enough? What is the impact of modern society on sleep? We spend about a third of our lives asleep. References to sleep abound in literature and art, sleep has been recognized as fundamental to the human condition. Over the past century, our knowledge of sleep has developed hugely. The impact of poor sleep on our quality of life is gaining recognition and the prevalence of sleep disorders in the population is increasing as we live ever stressful lives.