This study uses data from the CGS/GRE Survey of Graduate Enrollment and Degrees and a methodology that supports causal inference to examine the effects of affirmative action bans in Texas, California, Washington, and Florida on graduate student of color enrollment. The findings show that the bans have reduced by 12.2% the average proportion of graduate students who are underrepresented students of color. Given that graduate education is an important pathway for positions of power and influence in our nation, these findings have broad implications for higher education policies that seek to further national educational and democratic goals. They should also help inform legal determinations in cases concerning the constitutionality of affirmative action-related policies. (Contains 4 tables, 1 figure, and 6 footnotes.)