The Filth of Progress explores the untold side of a well-known American story. For more than a century, accounts of progress in the West foregrounded technological feats performed while canals and railroads were built, lionizing the railroad barons who financed the projects in the American West. This book salvages stories often omitted from the triumphant narrative of progress by focusing on the suffering and survival of the workers who were treated as outsiders. Ryan Dearinger examines the moving frontiers of canal and railroad construction workers in the tumultuous years of American expansion, from the completion of the Erie Canal in 1825 to the joining of the Central Pacific and Union Pacific railroads in 1869. He tells the story of the Irish and Chinese immigrants and the native-born citizens whose labor created the West's infrastructure and turned the nation's dreams of a continental empire into a reality. This book reveals that canals and railroads were not static monuments to progress but moving spaces of conflict and contestation.