The Music of the Spheres in the Western Imagination describes various systematic musical ecologies of the cosmos by examining attempts over time to define Western theoretical musical systems, whether practical, human, nonhuman, or celestial. This book focuses on the theoretical, theological, philosophical, physical, and mathematical concepts of a cosmic musical order and how these concepts have changed in order to fit different worldviews through the imaginations of theologians, theorists, and authors of fiction, as well as the practical performance of music. Special attention is given to music theory treatises between the ninth and sixteenth centuries, English-language hymnody from the eighteenth century to the present, polemical works on music and worship from the last hundred years, the Divine Comedy of Dante, nineteenth- and twentieth-century English-language fiction, the fictional works of C. S. Lewis, and the legendarium of J. R. R. Tolkien.