The US manufacturing sector came of age between 1870 and World War I. In 1870, the United States exported commodities and imported manufactured products. By the 1890s, US manufacturers were increasingly competitive in global markets, and commodities played a decreasing role in US exports. During this period, US tariff rates averaged 35 percent, providing significant shelter from international competition. Did tariffs boost US manufacturing productivity and help the United States emerge as a globally competitive manufacturing exporter? Our findings suggest they did not.