This chapter presents a new, annotated translation of the philosophical treatise Peri kosmou (often known by the Latin title De mundo), written in approximately the 1st century AD (a much-disputed date) and preserved among the works of Aristotle. The chapter introduction emphasizes the literary polish of the work, and the remarkable way in which it draws accurately upon a late hellenistic understanding of geography, the earth sciences, and cosmology in order to sustain its open-minded, but fundamentally Aristotelian and anti-Stoic, theological position and stimulate readers to immerse themselves more deeply in its philosophy.