From the first time they were dimly sighted through Galileo's telescope to the recent spectacular pictures beamed back by Voyager, Saturn's rings have fascinated generations of observers. The scientific problems associated with them have also attracted the attention of successive generations of theoreticians. James Clerk Maxwell's 1856 Adams Prize Essay, "On the Stability of the Motion of Saturn's Rings," forms the central body of this book and is the work that first established his reputation as one of the greatest mathematical physicists of any generation. It is surrounded by previously unpublished materials written both before and after the essay was completed. The former group consists of sixteen letters - to William Thomson (later Lord Kelvin), George Gabriel Stokes, Peter Guthrie Tait, and other friends and colleagues - written while Maxwell was working out the problems and preparing the essay for publication, and they reveal both the sureness of his approach and false starts and errors. The post-essay documents include a review of the work by George Biddell Airy, the Astronomer Royal, and correspondence with the Harvard astronomer George Bond in 1863. Here Maxwell attempts to extend his analysis to include the effects of collisions among the particles of the ring, employing his own newly developed kinetic theory of gases. The editors' introduction provides a historical context for Maxwell's contribution.