Humans have an internal clock that is never indifferent when we reorganize our lives. If external rhythms change, it may be disturbed for a short time. In the long run, it adjusts itself as soon as the external conditions stabilize again. However, if we continually override it, we can become ill. This book gathers much of what chronobiologists have discovered to date. It offers advice on how we can use this knowledge in our daily lives to stay healthy.