This course will cover fundamental theories on the regulation, evolution, and function of sleep-wake states – how and why animals sleep. Sleep is a behavioural state that occurs in all vertebrates and it has also been identified in several species of invertebrates. In these animals, sleep is associated with profound changes in physiological function at the molecular, cellular and system levels. Furthermore, sleep has marked implications for the neurobiology of behaviour and the evolution of organisms because of the impact it has on cognitive function, memory consolidation, and overall health. The course will be integrative and comparative, linking together concepts from all levels of biological organization (molecular to whole organism) and drawing examples from a variety of different animals.