This article explains the emergence and institutionalization of the US’s targeted killing practices as a case of norm transformation. I argue that international and domestic US prohibitions on assassination have not disappeared, but have changed as a result of practitioner-led changes in the conventions, technologies, and bureaucratic structures governing the use of force in counterterrorism activities. After discussing the limits of alternative explanations, and drawing inspiration from practice theory, pragmatist social theory, and relational sociology, I posit three causal mechanisms as responsible for the transformation: convention reorientation, which was the redefinition of targeted killing to distinguish it from assassination; technological revision, which was the development and use of unmanned aerial vehicles (“drones”) to bypass normative and strategic concerns over precision; and network synthesis, which was the support of the Bush administration and especially of the Obama administration, overruling dissenters from within the Central Intelligence Agency (who were often very highly placed). I trace the processes by which these mechanisms operated and interacted in simultaneous and mutually reinforcing ways from the start of the millennium until now. Finally, I discuss some of the ways in which this contributes to institutional analysis and the study of norm change more generally, and, in particular, how it considers the role of technology and the reciprocity of means and ends.