While much has been written on the ramifications of Newton\'s dynamics, until now the details of Newton\'s solution were available only to the physics expert. The Key to Newton\'s Dynamics clearly explains the surprisingly simple analytical structure that underlies the determination of the force necessary to maintain ideal planetary motion. J. Bruce Brackenridge sets the problem in historical and conceptual perspective, showing the physicist\'s debt to the works of both Descartes and Galileo. He tracks Newton\'s work on the Kepler problem from its early stages at Cambridge before 1669, through the revival of his interest ten years later, to its fruition in the first three sections of the first edition of the Principia.