Many areas of neuroscience have benefited from the upsurge in genomic and molecular biology in recent years. One prime example is the study of sleep. Insights into how our sleep–wake cycle is regulated have come from findings such as the identification of orexin as the affected protein in narcolepsy, and the genetic dissection of the circadian clock in both flies and mammals.

However, we cannot hope to elucidate the mysteries of sleep by molecular analysis alone. This month, on page 591, Edward Pace-Schott and J. Allan Hobson review the neurobiology of sleep from the point of view of its genetic, cellular and subcortical-network mechanisms. In our September issue, Hobson and Pace-Schott will complement this review with another that discusses the cognitive neuroscience of sleep. Bringing together findings from diverse techniques and disciplines, they summarize our current understanding of the control and function of sleep at many levels, from genetic to behavioural.

The questions addressed in these ambitious reviews are wide-ranging. Although we have long had at least some understanding of the regulation of circadian rhythms and of sleep onset, only recently have we started to see how these two systems might work together to govern our patterns of activity and sleep. Similarly, the control of sleep onset must interact with the ultradian rhythm that gives rise to cycles of rapid eye movement (REM) and non-REM sleep.

Many fundamental questions in sleep research remain unanswered. Perhaps the most fundamental of all — 'Why do we sleep?' — is still the subject of intense debate and controversy. But a multidisciplinary approach, as exemplified by these two reviews, is surely our best hope of answering these questions — and many others in neuroscience.