n 1907 the U.S. Congress created a joint commission to investigate what many Americans saw as a national crisis: an unprecedented number of immigrants flowing into the United States. Experts—women and men trained in the new field of social science—fanned out across the country to collect data on these fresh arrivals. The trove of information they amassed shaped how Americans thought about immigrants, themselves, and the nation’s place in the world. Katherine Benton-Cohen argues that the Dillingham Commission’s legacy continues to inform the ways that U.S. policy addresses questions raised by immigration, over a century later.