Counting conservatively, and ignoring physical injuries and mental trauma, data show about 100 million mass atrocity-related deaths since 1900. Occurring in war- and in peacetime, and of enormous scale, severity, and brutality, they are geographically widespread, occur with surprising frequency, and can be long-lasting in their adverse effects on economic and human development, wellbeing, and wealth. As such, they are a major economic concern. This article synthesizes very diverse and widely dispersed theoretical and empirical literatures, addressing two gaps: a “mass atrocities gap” in the economics literature and an “economics gap” in mass atrocities scholarship. Our goals are, first, for noneconomists to learn how economic inquiry contributes to understanding the causes and conduct of mass atrocities and possibly to their mitigation and prevention and, second, to survey and synthesize for economists a broad sweep of literatures to serve as a common platform on which to base further work in this field.