This chapter discusses Catharine A. MacKinnon’s theory of sex equality, its application as well as major strands of criticism. Beginning with a radical critique of liberal legalism, feminism and Marxism, MacKinnon conceived a hierarchy-centered theory of substantive equality, shifting the paradigm of equality thinking from questions of sameness and difference to the power structure of dominance and subordination. Drawing on feminist consciousness raising as method, her theory sees gender as an inequality and sexuality as the linchpin of gender inequality. It is also an engaged theory producing sex equality laws to address women’s sexual violations: sexual harassment as a legal injury and a form of sex discrimination; a harm-based civil-rights approach to pornography; an asymmetrical approach to the abolition of prostitution; and an inequality approach to rape as a gender-based crime. Against challenges from anti-essentialist and sex-positive critiques, MacKinnon’s theory embraces intersectionality as a method and pursues equality by resisting sexual oppression.