In the early 1930s, the International Ladies' Garment Workers' Union (ILGWU) organized large numbers of Black and Hispanic workers through a broadly conceived program of education, culture, and community involvement. The ILGWU admitted these new members, the overwhelming majority of whom were women, into racially integrated local unions and created structures to celebrate ethnic differences. This book revolves around this phenomenon of interracial union building and worker education during the Great Depression. Investigating why immigrant Jewish unionists in the ILGWU appealed to an international force of coworkers, the book traces their ideology of a working-class-based cultural pluralism, which it newly terms “mutual culturalism,” back to the revolutionary experiences of Russian Jewish women. These militant women and their male allies constructed an ethnic identity derived from Yiddish socialist tenets based on the principle of autonomous national cultures in the late nineteenth-century Russian Empire. The book offers a fresh perspective on the nature of ethnic identity and working-class consciousness and contributes to current debates about the origins of multiculturalism.