Drawing on original interviews with ex-insurgents and eyewitnesses of the Second Chechen War (1999-2009), this article develops a theory of "kin killing," defined as the use of lethal violence agaisnt insurgents' relatives as a deliberate counterinsurgency tactic. Family-based targeting works by coercing insurgents to surrender or defect, deterring insurgents' relatives from retaliation, and discouraging prospective recruits from joining or supporting insurgents. Because it targets a small number of individuals who have strong ties to insurgents, kin killing is the most selective form of collective violence. The tactic is most likely to be used by illiberal regimes that know the identity of the insurgents, but not their locations, and operate in traditional societies with large, tightly knit families. Most would consider kin killing - and its nonlethal counterpart, kin targeting - ethically reprehensible, but numerous countries have employed it with varying degrees of success, including Russia, the United Kingdom, and China. Militarily dominant regimes who employ kin killing can turn family members from force multipliers into pressure points for insurgents, as regimes "flip the network" and make restraint, rather than revenge, the best way to protect one's family.