Racial disparity in arresting behavior is a significant concern for people of color. It also delegitimizes law enforcement, increases tension between police and citizens, and can even increase crime. Efforts at police reform stall, in part because racial disparity in policing was previously unmeasurable. The authors present three new measures of racial disparity in arrest, measured across more than 13,000 agencies nationwide, allowing for reliable analysis of disparity across time and geographic space. These measures are validated against Department of Justice law enforcement misconduct investigations, the “gold standard” for assessing racial disparity in policing.