Johannes Kepler wrote Astronomia Nova (1609) in a singleminded drive to sweep away the ancient and medieval clutter of spheres and orbs and to establish a new truth in astronomy, based on physical causality. Thus a good part of the book is given over to a non-technical discussion of how planets can be made to move through space by physical forces. This is the theme of the readings in the present volume. In the selections chosen and translated by William Donahue, the true Kepler emerges, not as a speculative mystic or a number-crunching drudge, but as a first-rate scientific thinker with a wonderfully engaging narrative style.