Kepler’s Optics began as an attempt to give astronomical optics a solid foundation, but soon transcended this narrow goal to become a complete reconstruction of the theory of light, the physiology of vision, and the mathematics of refraction. This translation is accompanied by by extensive footnotes (not endnotes). Nearly all the diagrams were drawn anew for this edition. The two exceptions are reproductions of Kepler’s original illustrations, used where the sense of the text requires them. Kepler’s original index has been retained, supplemented by a second index prepared by the translator.