The Three Pillars (Harmonization, Replacement, and Justice) describe an ethical path forward and away from the use of nonhuman primates in harmful research and scientific use.Conducting nonhuman primate research in an ethical way that acknowledges their moral importance requires satisfying more rigorous guidelines and regulations modeled on those that apply to similarly vulnerable human subjects, especially children and incarcerated persons.This Element argues for the moral necessity of harmonizing human and nonhuman primate research ethics, regulations, and guidelines in a way that protects all primates, human and nonhuman.The authors call for the replacement of nonhuman primates in research with human-relevant methods that do not simply shift research onto other nonhuman animals, and challenge publics, governments, and scientific communities worldwide to implement justice in the selection and use of all research subjects.This title is also available as Open Access on Cambridge Core.