In response to disparities in postsecondary access, governments have enacted policies to facilitate the admission of traditionally underrepresented students. Known as affirmative action in the United States, the legal justification of this approach has varied. This article describes the legal and political history of affirmative action, the social justice and then diversity rationales, and the importance of state policies and institutions. The article focuses attention on the responses of three highly diverse US states -- Texas, California, and Florida -- to postsecondary affirmative action bans affecting their public flagship institutions. Each developed race-neutral achievement-oriented percentage plans intended to promote socioeconomic and racial diversity in their states' institutions; these approaches did not meet their intended aims. While inequality shows no sign of shrinking, US institutions and administrators must continue to adapt to a shifting landscape of state and federal policies poised to further curtail these diversity and social justice efforts.