Abstract
This chapter summarizes epidemiological insights into sleep and wake behaviour and covers the limited knowledge about its disorders, with special emphasis on psychiatry. The chapter systematically refers to the interdependencies of four different aspects in both sleep and wake: timing, duration, structure, and quality. It provides an overview of the current methods used in the field for studying this behaviour and predicts that longterm actimetry monitoring in everyday life will revolutionize research into both sleep and the circadian clock. The chapter argues that a stronger alliance between sleep research and circadian biology will help to better understand the different aetiologies of sleep disorders, as well as the relationships between sleep and disease. It is predicted that strengthening our consideration of sleep’s circadian regulation versus its societal constraints—together with improved light environments—will ameliorate many sleep problems. There is also a need to improve public education about sleep and the circadian clock to increase selfawareness of sleep, activity, and light behaviour on an individual level to prevent false selfdiagnoses due to misconceptions about sleep.