When should the United States and other members of the international community intervene to stop a government from harming its own citizens? Since World War II, the main standard for intervention has been the high bar of genocide, although the international community has rarely acted to stop it. The main alternative—the “responsibility to protect”—would set the bar so low that virtually every instance of anarchy or tyranny would create unbounded obligations beyond the capacity of states to fulfill. A new standard—the pragmatic standard of humanitarian intervention—can help guide decisionmakers on when to intervene to stop governments from targeting their own citizens. The standard has three requirements: (1) an ongoing campaign of mass homicide sponsored by the government; (2) a viable plan for intervention with reasonable estimates of low casualties for the intervening forces; and (3) a workable strategy for creating lasting local security for the threatened population. The pragmatic standard was met in the recent successful intervention in Libya as well as in other cases over the last twenty years, and it should become the basis for deciding which humanitarian crises justify international intervention in the future.