In the words of one of his English contemporaries, Louis Pasteur was ”the most perfect man who ever entered the kingdom of science.” His contributions to the development of microbiology and medicine were profound, both practically (Pasteurization and vaccination) and theoretically (the germ model of disease). He spoke out forcefully on issues of the day, especially when they concerned public health, and his research included studies on rabies, anaerobic life, childbirth fever, silkworms, and beer. René Dubos’s outstanding biography examines Pasteur’s manifold genius in the context of the era—Pasteur was an exemplary nineteenth-century bourgeois—and in light of recent environmental thought. His view of Pasteur as ecologist, the first to formulate in concrete terms a biological and chemical theory of global ecosystems, is only one of the many surprising insights into a man whose emblematic fame has obscured a complex and rich life.