Police are one of the only institutions in the United States allowed to use force to coerce civilian compliance with laws and government decisions. In some cases, force—even fatal force—is needed to maintain the safety of the general public. But too often, excessive force is used against civilians, and this is the target of current police reform efforts in the United States. Sustained attention to and momentum toward reducing police killings had been lacking until May 2020, when the highly publicized murder of George Floyd was committed. Contributing to the current national conversation, this report summarizes what is currently known about killings committed by police in the United States and identifies existing evidence about various ways to prevent them.