When Horace Greeley published his famous imperative, "Go West, young man, and grow up with the country," the frontier was already synonymous with a distinctive type of idealized American masculinity. But Greeley's exhortation also captured popular sentiment surrounding changing ideas of American boyhood; for many educators, politicians, and parents, raising boys right seemed a pivotal step in securing the growing nation's future. This book revisits these narratives of American boyhood and frontier mythology to show how they worked against and through one another--and how this interaction shaped ideas about national character, identity, and progress. The intersection of ideas about boyhood and the frontier, while complex and multifaceted, was dominated by one arresting notion: in the space of the West, boys would grow into men and the fledgling nation would expand to fulfill its promise. Frontiers of Boyhood explores this myth and its implications and ramifications through western history, childhood studies, and a rich cultural archive. Detailing surprising intersections between American frontier mythology and historical notions of child development, the book offers a new perspective on William "Buffalo Bill" Cody's influence on children and childhood; on the phenomenon of "American Boy Books"; the agency of child performers, differentiated by race and gender, in Wild West exhibitions; and the cultural work of boys' play, as witnessed in scouting organizations and the deployment of mass-produced toys. These mutually reinforcing and complicating strands, traced through a wide range of cultural modes, from social and scientific theorizing to mass entertainment, lead to a new understanding of how changing American ideas about boyhood and the western frontier have worked together to produce compelling stories about the nation's past and its imagined future.