Close to seventeen million people in the United States, approximately 6 percent of the total population, identified themselves as Italian Americans in the 2016 census. Constituting the nation’s fifth largest ancestry group, they are the descendants of one of the greatest diasporas in human history. Since 1860, twenty-nine million Italians have left their homeland for better opportunities worldwide. Close to six million of them have settled in the United States with about five million arriving prior to World War I. Along with other European groups of the great transatlantic migrations of 1870–1920—Jews, Poles, Croatians, and Finns—they became an essential part of the American working class, building, shaping, and enriching its life and culture. Among the most ubiquitous of the early foreigners, Italians were initially confined to unskilled and manual jobs but gradually made their way into the ranks of semi-skilled operatives in mass-production manufacturing. By 1910, they constituted a vital segment of the American multinational workforce in the mining, garment, and steel industries and played key roles in the labor struggles of the early 20th century, providing both key leadership and mass militancy. Like other ethnic groups, Italian immigrant workers lived deeply transnational lives. Their class consciousness was continually informed by their ethnic identity and their complicated relationship to both Italy and the United States, as they sought to transform, and were transformed by, the political events, industrial conditions, and cultures of the two countries. The story of how Italian immigrant workers became “American” sheds light not only on their experience in the United States but also on the transnational character of the labor movement and the interplay of class, race, gender, and ethnic identities.