What explains the rise of race-conscious affirmative action policies in undergraduate admissions? The dominant theory posits that adoption of such policies was precipitated by urban and campus unrest in the North during the late 1960s. Based on primary research in a sample of 17 selective schools, we find limited support for the dominant theory. Affirmative action arose in two distinct waves during the 1960s. A first wave was launched in the early 1960s by northern college administrators inspired by nonviolent civil rights protests in the South. A second wave of affirmative action emerged in the late 1960s, primarily as a response to campus-based student protests. Most late-adopting schools were those most favored by the Protestant upper class. Our findings are most consistent with a theoretical perspective on institutional change in which social movements' effects are mediated by the moral and ideological beliefs of key administrators.