This dissertation explores how tens of thousands of working women in the Young Women’s Christian Association industrial clubs reworked the YWCA’s Christian mission and forged a nationwide movement of faith-driven working-class activism. They drew on an ideology of “Christian sisterhood” and of labor solidarity to organize across extraordinary differences of race, ethnicity, region, political belief, and even religious background. My study restores religion as a crucial aspect of working-class and women’s history in the twentieth century, and extends exploration of how Christian faith has helped ordinary people overcome deeply held prejudices and have the courage to challenge social injustices.