Why have African-American private-sector unionization rates surpassed those of white workers for decades, and how has private-sector union decline exacerbated black-white wage inequality? Using data from the Current Population Survey (1973–2007), the authors show that African-Americans join unions for protection against discriminatory treatment in nonunion sectors. A model-predicted wage series also shows that, among women, black-white weekly wage gaps would be between 13% and 30% lower if union representation remained at high levels. The effect of deunionization on racial wage inequality for men is less substantial, but without deunionization, weekly wages for black men would be an estimated $49 higher. The results recast organized labor as an institution vital for its economic inclusion of African-American men and women. This study points to the need to move beyond class-based analyses of union decline to an understanding of the gendered role unions once played in mitigating racial inequality.