Intersectionality is a macrostructural theory that highlights the co-constitutiveness of multiple systems of oppression, e.g., race, gender, class, sexuality, gender identity, ability, language, and nationality. It focuses in particular on how these systems of oppression interlock to maintain the power and status of elites and to differentially disadvantage individuals and groups based on their position within and across structures. It is rooted in the theorizations and activism of black women, who interrogated their statuses as disadvantaged by both race and gender and thus challenged their erasure from consideration in movement politics and goals. As a sociological theory of structural inequality, it accounts for how disadvantage is distributed throughout society, complicating traditional sociological notions of strictly hierarchical forms of inequality. Beyond sociology, it is a theoretical tool of both the personal and the political, the micro and the macro, informing conceptualizations of representation, discourse, identity, and inequality. This chapter chronicles intersectionality's origins in enslaved black women's thought; its disciplinary beginnings in the work of late nineteenth and early twentieth century black sociologists; its modern roots in the radical, civil rights, and women's liberation movements; its theoretical refinement in the scholarship of black feminist thinkers; its canonical adoption in sociology; its emergence as a popular theory in public and movement discourse; and its black feminist legacies.