Kepler is remembered for the 3 laws of planetary motion known after him. Rejecting the view of those who regarded astronomical hypotheses as mathematical fictions, he sought to derive the true motions of the planets from physical causes. Yet he combined his search for physical causes with a vision of the world as a manifestation of divine harmony. This led him to consider the formal causes or archetypes underlying the world's construction. Kepler's favorite astronomical work, Harmony of the World (HW), was planned in 1599, although it was not completed and published until 1619. Here, the translators have put the HW into the kind of clear but earnest language which they suppose Kepler would have used if he had been writing today. Illustrations.