Violent conflict between states has declined over the years, but conflict between individual groups waving the banner of ethnicity has risen. When does ethnicity crowd out other identities (such as state, society, tribe, or nation) and trigger conflict? This anthropological study finds only complicated and tentative answers. Its central premise is that ethnic identity is subjective, based on beliefs about a common ancestry or shared historical past. From this assumption, Eller argues that ethnicity can be lost, discovered, or simply invented. Leaders who pursue practical and unsentimental agendas of power can easily exploit culture, myths, and historical memory. Taking as case studies Sri Lanka, Rwanda, Burundi, Bosnia, Quebec, and the Kurds, Eller successfully illustrates the diversity and nuances of ethnicity. But his lack of a more sweeping conclusion will frustrate readers searching for a general thesis on ethnicity and the sources of ethnic conflict.