Efficiency--associated with individual discipline, superior management, and increased profits or productivity--often counts as one of the highest virtues in Western culture. But what does it mean, exactly, to be efficient? How did this concept evolve from a means for evaluating simple machines to the mantra of progress and a prerequisite for success? In this provocative and ambitious study, Jennifer Karns Alexander explores the growing power of efficiency in the post-industrial West. Examining the ways the concept has appeared in modern history--from a benign measure of the thermal economy of a machine to its widespread application to personal behaviors like chewing habits, spending choices, and shop floor movements to its controversial use as a measure of the business success of American slavery--she argues that beneath efficiency's seemingly endless variety lies a common theme: the pursuit of mastery through techniques of surveillance, discipline, and control. Six historical case studies--two from Britain, one each from France and Germany, and two from the United States--illustrate the concept's fascinating development and provide context for the meanings of, and uses for, efficiency today and in the future.