Le Monde represents Descartes's first attempt at a comprehensive treatment of natural philosophy. The unfinished text, written between 1630 and 1633, was published after his death. As he was preparing its publication, he learned of the conviction of Galileo Galilei, who had been "guilty" of defending the motion of the Earth. Since this thesis was one of the fundamental premises that Descartes defended in Le Monde, he put the text in a drawer. The text was first published in 1664 under Le Monde ou le traité de la lumière (the first fifteen chapters of Le Monde).

In this work, Descartes sets himself the task of explaining the phenomenon of light in a mechanistic way, i.e. on the basis of the forms and movements of the bodies that constitute it. In doing so, he relies on a geometrical conception of matter, or the three elements (fire, air, earth), and gives a theory of the three fundamental laws of motion. In accordance with these concepts, it gives a hypothetical explanation of the origin and functioning of the fundamental cosmological entities (heavens, stars, planets and comets) and phenomena (gravity and tides) and finally explains the nature and properties of light. Since the outlines of the later Principia philosophiae can often be detected in the physical theses of Descartes' Le Monde, a reading of Le Monde is indispensable for an understanding of the development of Descartes' philosophy of nature.