Given his energetic involvement in practical initiatives and extensive lecturing, Rudolf Steiner had little time to write books. Of those he did write - belonging almost entirely to the earlier years of his work - four titles form an indispensable introduction to his later teaching: Knowledge of the Higher Worlds, Theosophy, The Philosophy of Freedom and Occult Science. The anthroposophy of Rudolf Steiner is not a theoretical system, but the results of research based on direct observation. As Steiner's research was so vast and conducted over such a long period of time, no single book can be said to contain the whole of his spiritual teaching. However, of all his books Occult Science comes closest. Steiner even referred to it as 'an epitome of anthroposophical spiritual science'. The book sets out, in systematic order, the fundamental facts concerning the nature and constitution of the human being and, in chronological order, the history of the universe and man. Whereas the findings of natural science are derived from observations made through the senses, the findings of spiritual science, or anthroposophy, are 'occult' inasmuch as they derive from direct observation of realities which are hidden to everyday perception. And yet these elements of humanity and the universe form the foundation of the sense world. A substantial part of Occult Science is occupied by a description of the preliminary training which is necessary to make such spiritual observations. Although Occult Science is not all-inclusive, it is indispensable to any serious student seeking to master Rudolf Steiner's extraordinary philosophy.