Despite a considerable amount of anthropological research into the phenomena of blood revenge and blood feud, little is known about the role of blood revenge as a cause of violent mobilization in irregular wars. Blood revenge, or the practice of seeking blood retribution for a grave offense committed against an individual or his or her relatives, has been practiced since the dawn of humankind. In recent years, it has functioned as an important apolitical mechanism in encouraging violent mobilization in irregular wars, including against foreigners. Scholars in disciplines as varied as anthropology, sociology, psychology, and criminology have explored the phenomenon of blood revenge in depth. In his seminal work on blood revenge among Yanomamo tribes of the Amazon ba- sin, Napoleon Chagnon stated that “[b]lood revenge is one of the most com- monly cited causes of violence and warfare in tribal societies.” 1 More recently, some scholars have examined the practice of blood revenge in conºict-ridden societies, including those in Albania, Chechnya, Yemen, and Colombia. 2 Over- all, however, the literature on political violence and conºict studies has yet to offer a comprehensive, systematic empirical account of how blood revenge manifests itself in contemporary irregular wars. In contrast to the literature on blood revenge in tribal or premodern warfare and on blood revenge as a form of social violence and social justice, 3 this study argues that blood revenge has much wider application in conºict environ- ments than scholars have generally assumed. We empirically ground this proposition in a contextualized and systematic examination of blood revenge practices during the anti-Russian insurgencies in Chechnya from the mid- 1990s to the mid-2000s. We begin by conceptualizing the term “blood revenge.” Drawing insights from the extensive literature on blood revenge in anthropology, ethnography, and sociology, we then examine the theoretical implications of blood revenge for the discipline of conºict studies. This section also analyzes the impor- tance of blood revenge in several major present-day irregular wars, including those in Afghanistan, Iraq, Yemen, and Somalia. Next, we categorize blood re- venge as an apolitical, grievance-driven cause of violent mobilization in irreg- ular wars. A section on methods and data these conceptual and theoretical sections. The subsequent empirical sections present our case study and report International Security, Vol. 40, No. 2 (Fall 2015), pp. 1–, doi:10.1162/ISEC_a_00219 © 2015 by the President and Fellows of Harvard College and the Massachusetts Institute of Technology. Blood Revenge and Violent Mobilization Blood Revenge and Violent Mobilization Emil Aslan Souleimanov and Huseyn Aliyev Evidence from the Chechen Wars 1