In 1686 Edmond Halley received the manuscript of the Principia from Isaac Newton and several years later predicted the return of the comet that now bears his name using Newton's law of universal gravitation. In 1986 Halley's comet made its fourth appearance since its prediction. These landmark events marking the spectacular achievements of Newton and Halley provide the framework for a reexamination of the circumstances surrounding them. In this volume, eighteen distinguished scholars, including astronomers, physicists, philosophers, and historians of science from several countries, present both new material and fresh interpretations of familiar topics, all considered from humanistic and philosophical vantage points. For decades scholars have been puzzled by Halley's publication at his own expense of Newton's Principia, and by Newton's subsequent relationship with his younger contemporary. The distinguished contributors to this volume not only grapple with these questions but examine such matters as patronage and institutions as well as some of the scientific advances in astronomy, surveying, mechanics, and mathematics that were made possible by Newton and Halley's professional association.