Sleep is one of the greatest riddles of existence. It is an absolute necessity for the refreshment of each one of us, yet natural science can give virtually no explanation of how this is done. And the reason for this is clear – it is not only a natural but primarily also a spiritual process. Understanding therefore depends on the research of the spiritual scientist, and pre-eminently on that of Rudolf Steiner. This book is the first integrated account of the many aspects of sleep which Steiner described, and the first to outline in anthroposophical terms the bodily processes involved.