Kepler is a key figure in the development of modern astronomy. His work is also important in the history of philosophy and methodology of science as a whole. The present study is concerned with one of Kepler's major preoccupations, namely his search for the geometrical plan according to which God created the Universe. The author discusses how Kepler's cosmological theories, which embrace music and astrology as well as astronomy, are related to his other work. The subject will be of great interest to historians of science, mathematicians and astronomers as well as to historians of the late Renaissance.