Kepler's successful solution to the problem of vision early in the 17th century was a theoretical triumph as significant as many of the more celebrated developments of the scientific revolution. Yet the full import of Kepler's arguments can be grasped only when they are viewed against the background of ancient, medieval, and Renaissance visual theory. David C. Lindberg provides this background, and in doing so he fills the gap in historical scholarship and constructs a model for tracing the development of scientific ideas.