"Do not think of the Pennsylvania Railroad as a business enterprise," Forbes magazine informed its readers in May 1936. "Think of it as a nation." At the end of the nineteenth century, the Pennsylvania Railroad was the largest privately owned business corporation in the world. In 1914, the PRR employed more than two hundred thousand people—more than double the number of soldiers in the United States Army. As the self-proclaimed "Standard Railroad of the World," this colossal corporate body underwrote American industrial expansion and shaped the economic, political, and social environment of the United States. In turn, the PRR was fundamentally shaped by the American landscape, adapting to geography as well as shifts in competitive economics and public policy. Albert J. Churella's masterful account, certain to become the authoritative history of the Pennsylvania Railroad, illuminates broad themes in American history, from the development of managerial practices and labor relations to the relationship between business and government to advances in technology and transportation. Churella situates exhaustive archival research on the Pennsylvania Railroad within the social, economic, and technological changes of nineteenth- and twentieth-century America, chronicling the epic history of the PRR intertwined with that of a developing nation.