One of Rudolf Steiner's most important contributions to our understanding of the world was in the field of angelology -- in the description and understanding of the work of spiritual beings, nature spirits, and elementals in the cosmos. In this classic, unparalleled work of angelology (one of only two lecture cycles he gave on the subject), Steiner leads the reader from sense experiences to the experience of the spiritual beings active in nature and the elements and forces of the earth, and to the dynamic, cosmic working of the angelic hierarchies. He unfolds a magnificent vision of the collaboration of hierarchical beings in cosmic and human evolution, and shows how human beings, as angelic beings, participate in this process as the Tenth Hierarchy.