Economists have traditionally taken two very different approaches to studying market structure. One looks to "industry characteristics" to explain why different industries develop in different ways; the other looks to the pattern of firm growth within a "typical" industry to describe the evolution of the size distribution of firms. In his new book, John Sutton sets out a unified theory that encompasses both approaches, while generating a series of novel predictions as to how markets evolve. Using statistical analysis and a detailed examination of industry histories, he rigorously tests...