This chapter describes the shocking yet puzzling characteristics of Rwanda’s violence that have marked it as a world-historical event and made it a key case for those interested in the study of genocides and mass killings. It offers the reader a review of the many competing theories for how and why genocides occur and also for how and why individuals come to participate in them. It also sets out the current scholarly consensus on these two questions in relation to Rwanda and highlights the various debates that remain unresolved despite the expansive scholarship on Rwanda. The chapter then offers an executive summary of the argument presented in the book and, in anticipation of the potentially polarized and politicized reaction that scholarship on the genocide often generates, a detailed exposition of the methods and evidence relied on to build this argument.