Abstract: This paper examines the impact on agricultural development of the introduction of barbed wire fencing to the American Plains in the late nineteenth century. Without a fence, farmers risked uncompensated damage by others’ livestock. From 1880 to 1900, the introduction and near-universal adoption of barbed wire greatly reduced the cost of fences, relative to the predominant wooden fences, especially in counties with the least woodland. Over that period, counties with the least woodland experienced substantial relative increases in settlement, land improvement, land values, and the productivity and production share of crops most in need of protection. This increase in agricultural development appears partly to reflect farmers’ increased ability to protect their land from encroachment. States’ inability to protect this full bundle of property rights on the frontier, beyond providing formal land titles, might have otherwise restricted agricultural development. (c) 2010 by the President and Fellows of Harvard College and the Massachusetts Institute of Technology..