When the 2014 police shooting of Michael Brown in Ferguson, Missouri, set off riots, we knew very little about the true number of people killed by American law enforcement. But since that time, private actors have stepped up efforts to count such killings comprehensively—and to collect some basic details about each incident. These data, along with agency-specific information furnished by police departments, have facilitated a massive amount of research into an important question: whether there is racial bias in police officers’ use of lethal force.