Why are people who work anti-social shifts more illness prone and die younger? What is jet-lag and can anything help? Why do teenagers refuse to get up in the morning and are the rest of us really ‘larks’ or ‘owls’? Why are most people born (and die) between 3am and 5am? And should patients be given medicines (and operations) at set times of the day, because the body reacts so differently in the morning, evening and night? The answers lie in our biological clocks, the mechanisms which give order to all living things.