"'To explore and explain the development of Kepler's planetary theory, and of the physical hypotheses integral to that theory, more faithfully than has yet been done'--is [Stephenson's] expressed aim in this book. He has achieved it in a way unlikely to be surpassed; a more lucid and thorough account is scarcely imaginable. A good deal that was previously murky is here made clear. For an understanding of Keplerian endeavor 'from the inside,' Stephenson's book is undoubtedly the best guide now available."--Curtis Wilson, Centaurus "A landmark contribution to Keplerian studies and one that must not be missed by any historian or astronomer who seeks an understanding of the genesis of Kepler's laws."--Owen Gingerich, Isis