Women earn nearly half of doctoral degrees in research fields, yet doctoral education in the United States remains deeply segregated by gender. We argue that in addition to the oft-noted segregation of men and women by field of study, men and women may also be segregated across programs that differ in their prestige. Using data on all doctorates awarded in the United States from 2003 to 2014, field-specific program rankings, and field-level measures of math and verbal skills, we show that (1) "net" field segregation is very high and strongly associated with field-level math skills; (2) "net" prestige segregation is weaker than field segregation but still a nontrivial form of segregation in doctoral education; (3) women are underrepresented among graduates of the highest-and to a lesser extent, the lowest-prestige programs; and (4) the strength and pattern of prestige segregation varies substantially across fields, but little of this variation is associated with field skills.Keywords: gender segregation; prestige segregation; field segregation; gender inequality; higher education; women in STEM W OMEN earn 60 percent of baccalaureate degrees and 46 percent of doctoral degrees in research fields (National Science Foundation [NSF] 2015a), yet higher education in the United States remains deeply segregated by gender. To date, the literature on educational segregation has focused on the distribution of men and women across fields of study, how this distribution varies over time and space, and its consequences for gender inequality in career outcomes Bradley 2002, 2009;England and Li 2006;England et al. 2007;Barone 2011;Bobbitt-Zeher 2007; DiPrete 2013, 2016; NSF 2015b;Ransom 1990). We extend this line of research by offering a multidimensional analysis of segregation in doctoral education across fields of study and across PhD-granting programs that differ in their prestige.Our interest in prestige segregation stems from four sources. At the most basic level, prestige segregation, like field segregation, is an indicator of the extent to which men and women's educational outcomes are equal. However, the two types of segregation are conceptually and empirically distinct. Even in a hypothetical world in which every field graduates the same proportions of men and women, men may be overrepresented among degree recipients from the highest ranked programs and women among degree recipients from the lowest ranked programs. In this world, gender integration exists with respect to field, but not with respect to program prestige.Second, field and prestige segregation represent two qualitatively different forms of gender inequality in higher education. Prestige segregation is inherently vertical, meaning that segregation occurs across categories that are ordered from 123 Weeden, Thébaud, and Gelbgiser Degrees of Difference high to low. Field segregation, by contrast, is horizontal: the boundaries between fields define qualitatively different positions, but fields "represent distinctions more of kind than of grade" (Cha...